fix: fallback to default test data path if GAR_TEST_DATA not set

[bhavish00007]

Reason for this PR

Fixes #757

Currently, the test data path for Spark testing is read solely from the GAR_TEST_DATA environment variable. This creates friction for new contributors or developers running tests locally without a custom setup.

This PR proposes a fallback to automatically detect common default locations (testing/, ../testing/, ../../testing/) in case the environment variable or system property is not set.

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What changes are included in this PR?

• Enhanced the checkTestData() method to:
  • First check GAR_TEST_DATA environment variable
  • Then check Java system property gar.test.data
  • Finally fallback to check common local paths for test data directories (like testing/, etc.)
• Ensures ldbc_sample/csv/ldbc_sample.graph.yml exists before accepting the path

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Are these changes tested?

These changes reuse the existing validation logic already in place within checkTestData(). The fallback will only apply if GAR_TEST_DATA is not set, so no changes are required in the test suite itself.

Manually tested by running without the environment variable and verifying that the fallback path works correctly.

---

Are there any user-facing changes?

No. This only impacts the developer testing experience. No changes to APIs or public behavior.

[yangxk1]

Hi @bhavish00007 , please note that this PR is not ready yet

[bhavish00007]

@yangxk1 can u give me update when its ready

[yangxk1]

@bhavish00007, the check ci were failed, please format code (run mvn spotless:apply)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.00%. Comparing base (1bb0468) to head (76f0bb8).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #758      +/-   ##
============================================
+ Coverage     77.77%   82.00%   +4.22%     
- Complexity      234      299      +65     
============================================
  Files            25       25              
  Lines           918     1000      +82     
  Branches         49       84      +35     
============================================
+ Hits            714      820     +106     
+ Misses          167      125      -42     
- Partials         37       55      +18     

Flag	Coverage Δ
java-info	82.00% <ø> (?)

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[yangxk1]

Hey @bhavish00007 , I formatted the code and pass the test, It looks good. Do you have anything else to add?

[yangxk1]

Does this PR resolve the issue? @Thespica