fix(git): improve diff handling and code quality in GitDataStore

[marevol]

Summary

Fix incorrect path resolution for deleted files in diff processing and improve overall code quality in GitDataStore.

Changes Made

• Fix DELETE diff handling: Use getOldPath() instead of getNewPath() for DiffEntry.ChangeType.DELETE entries, since deleted files have no new path
• Support auto-adding PREV_COMMIT_ID: When PREV_COMMIT_ID is not present in handler parameters, append it automatically so incremental crawling works on first run
• Scope git log query: Pass currentCommitId to git.log().add() in getRevCommit() to ensure log is scoped to the correct commit
• Fix logging: Replace string concatenation with SLF4J parameterized logging ({}) in logger.warn() calls
• Simplify temp directory creation: Use Files.createTempDirectory() instead of manual createTempFile + delete + mkdir sequence
• Remove dead code: Remove unused isUpdateCommitId variable and redundant configMap.put(REPOSITORY, repository) call

Testing

• Verified compilation succeeds with mvn compile

Breaking Changes

• getRevCommit() method signature now includes throws IOException — subclasses overriding this method will need to update their signature

Additional Notes

• The DELETE path fix is important for incremental crawling scenarios where files are removed between commits
• The updateDataConfig change enables seamless first-run behavior without requiring manual PREV_COMMIT_ID configuration