test: Add missing coverage for chunking module edge cases

[vedssharma]

Adds tests for untested guard clauses (IndexError/ValueError/TokenUtilError error paths), ChunkIterator constructor fallbacks, TextChunk property raises and caching behavior, _sanitize, make_batches_of_textchunk batch sizes, and the broken_sentence flag reset logic. addresses issue #430

[github-actions]

No linked issues found. Please link an issue in your pull request description or title.

Per our Contributing Guidelines, all PRs must:

• Reference an issue with one of:
  • Closing keywords: Fixes #123, Closes #123, Resolves #123 (auto-closes on merge in the same repository)
  • Reference keywords: Related to #123, Refs #123, Part of #123, See #123 (links without closing)
• The linked issue should have 5+ 👍 reactions from unique users (excluding bots and the PR author)
• Include discussion demonstrating the importance of the change

You can also use cross-repo references like owner/repo#123 or full URLs.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[github-actions]

⚠️ Branch Update Required

Your branch is 1 commits behind main. Please update your branch to ensure CI checks run with the latest code:

git fetch origin main
git merge origin/main
git push

Note: Enable "Allow edits by maintainers" to allow automatic updates.