Expose failed commit count and exceptions in BaseCommitService

[erkanonl]

What does this change do?

This PR adds lightweight tracking for failed commit attempts in BaseCommitService.

Specifically, it:

• Counts the number of failed commit attempts during rewrite actions
• Captures the exceptions thrown by failed commits for diagnostic purposes
• Exposes this information via accessor methods for use by callers and tests

Why is this change needed?

BaseCommitService explicitly supports partial progress, but today failed commits are only logged.
This makes it difficult to:

• Programmatically detect partial failures
• Surface useful diagnostics to callers
• Write tests that assert failure behavior without relying on log inspection

This change improves observability without altering commit behavior or public APIs.

Scope and compatibility

The change is limited to BaseCommitService, which is package-private and internal
No behavioral changes to commit execution or error handling
No impact on existing public APIs

[erkanonl]

Closing in favour of #14872