[Feat] Explicit definition override

[arnaudgiuliani]

Add Explicit Override DSL (4.2.0-alpha2)

Summary

Adds fine-grained override control at the definition level, allowing specific definitions to override others even when global allowOverride(false) is enabled.

Changes

Core Feature:

• New .override() DSL function for explicit per-definition override marking
• Works with both fluent syntax (.override()) and withOptions { override() }
• BeanDefinition.allowOverride: Boolean? property to track override flag
• Updated InstanceRegistry to check definition-level override flag

API:

  startKoin {
      allowOverride(false)  // Strict mode
      modules(
          module { single<Service> { ProductionService() } },
          module { single<Service> { TestService() }.override() }  // ✅ Allowed
      )
  }

Use Cases:

• Test configurations overriding production services
• Feature flags conditionally overriding implementations
• Plugin systems where specific plugins can override defaults

Documentation

• Added comprehensive KDoc for all new functions
• Updated docs: modules.md, definitions.md, dsl.md
• Cross-references and examples included

Testing

• ExplicitOverrideTest.kt with full coverage
• Tests both .override() syntax and withOptions syntax
• Tests binding scenarios

Version

Bumped to 4.2.0-alpha2