feat: add stacSliverPadding widget, parser,example and documentation

[akhil-ge0rge]

Description

This PR introduces support for stacSliverPadding by adding a new widget model and its corresponding parser.

Related Issues

Closes #417

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Code refactor
• Build configuration change
• Documentation
• Chore

Summary by CodeRabbit

• New Features

  • Added SliverPadding widget support for applying padding inside scrollable layouts (CustomScrollView).

• Documentation

  • Added a docs page describing SliverPadding with properties and a usage example.

• Examples

  • Added a gallery entry and an example showcasing a padded sliver containing a styled box.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a new StacSliverPadding model, JSON (de)serialization, parser, parser registration and export, WidgetType enum entry, documentation page, and an example + gallery navigation entry for SliverPadding.

Changes

Cohort / File(s)	Summary
Documentation & Examples docs/docs.json, docs/widgets/sliver_padding.mdx, examples/stac_gallery/assets/json/home_screen.json, examples/stac_gallery/assets/json/sliver_padding_example.json	Add docs entry and MDX page for SliverPadding; add gallery home list item and a new example JSON demonstrating a SliverPadding wrapping a SliverToBoxAdapter.
Core Model & Serialization packages/stac_core/lib/widgets/sliver_padding/stac_sliver_padding.dart, packages/stac_core/lib/widgets/sliver_padding/stac_sliver_padding.g.dart, packages/stac_core/lib/widgets/widgets.dart	Add StacSliverPadding StacWidget model with padding and sliver fields, generated JSON (de)serializers, and export from widgets barrel.
Widget Type & Enum packages/stac_core/lib/foundation/specifications/widget_type.dart	Insert new enum value sliverPadding into WidgetType.
Parser & Service Registration packages/stac/lib/src/parsers/widgets/stac_sliver_padding/stac_sliver_padding_parser.dart, packages/stac/lib/src/parsers/widgets/widgets.dart, packages/stac/lib/src/framework/stac_service.dart	Add StacSliverPaddingParser, export it, and register it in StacService parser list to enable runtime JSON → SliverPadding widget parsing.

Sequence Diagram(s)

sequenceDiagram
    participant JSON as JSON asset
    participant Service as StacService
    participant Parser as StacSliverPaddingParser
    participant Model as StacSliverPadding
    participant Flutter as Flutter SliverPadding

    JSON->>Service: load JSON
    Service->>Parser: dispatch by type ("sliverPadding")
    Parser->>Model: getModel(json)
    Parser->>Parser: construct StacSliverPadding
    Parser->>Flutter: parse(context, model) -> SliverPadding widget
    Flutter->>Flutter: render inside CustomScrollView

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• chore: Release Stac 1.0.0-dev.7 #355: Changes exports and StacEdgeInsets parser/export that this PR's model depends on — potential code-level overlap or conflict.

Suggested reviewers

• divyanshub024
• Potatomonsta

Poem

🐰
I hopped through JSON, tidy and bright,
Wrapped a sliver snug in soft padding light,
Parsers hum, docs sparkle, examples play,
A little box lounges in green all day,
Nibble nibble — code hops on its way! 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: adding a stacSliverPadding widget, parser, example, and documentation.
Linked Issues check	✅ Passed	The PR fully implements the requirement from issue #417 to create StacSliverPadding as the StacWidget equivalent of Flutter's SliverPadding.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing StacSliverPadding support: the widget model, parser, example, documentation, and necessary registrations. No unrelated changes detected.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@examples/stac_gallery/assets/json/home_screen.json`:
- Around line 1250-1253: Update the "subtitle" value in the JSON entry for the
SliverPadding tile (the "subtitle" property) to remove the incorrect "Material
Design" qualifier; replace "A Material Design Sliver Padding widget" with a
concise, accurate phrase such as "A Flutter SliverPadding widget" or "A
SliverPadding widget" so it correctly reflects that SliverPadding is from
Flutter's widgets library.

In `@packages/stac_core/lib/widgets/sliver_padding/stac_sliver_padding.dart`:
- Around line 22-48: The JSON example in the documentation block of
stac_sliver_padding.dart uses // single-line comments so it won't be picked up
by doc generation; update the JSON lines inside the fenced comment (the block
between ```json and ```) to use Dart doc comment markers (///) instead of // so
the example is included in generated docs — i.e., replace each leading // with
/// for the JSON object lines in the sliverPadding example.

🧹 Nitpick comments (1)

packages/stac/lib/src/parsers/widgets/stac_sliver_padding/stac_sliver_padding_parser.dart (1)

4-4: Unused import.

The stac_edge_insets_parser.dart import appears unused. The model.padding.parse getter is provided by StacEdgeInsets (from stac_core), not by the parser.

🔧 Suggested fix

 import 'package:flutter/material.dart';
 import 'package:stac/src/parsers/core/stac_widget_parser.dart';
-
-import 'package:stac/src/parsers/foundation/geometry/stac_edge_insets_parser.dart';
 import 'package:stac_core/stac_core.dart';
 import 'package:stac_framework/stac_framework.dart';

[akhil-ge0rge]

Hi @divyanshub024 , @Potatomonsta 👋,
Please take a look. Thanks!