Fix program_html evaluator race condition and empty string handling

[Tharun-Varshan-S]

Resolves #407

This PR implements the fixes suggested in #407:

1. Replaces the hardcoded time.sleep(3) with page.wait_for_load_state("networkidle"), explicitly catching and tolerating TimeoutError so we evaluate pages with heavy background activity gracefully.
2. Updates the except Exception blocks for the JS locators to assign selected_element = None (instead of ""), ensuring missing elements correctly hit the is None guard and return 0.0 directly rather than vacuously slipping through to the string scorers.
3. Adds mocked regression tests for these edge cases.

[Surya-5555]

Hi @Tharun-Varshan-S - Thanks for the PR
It looks like the code-format check is failing. Could you please run pre-commit locally and push the formatting updates?
Looking forward to reviewing this once the checks are green

[Tharun-Varshan-S]

Hi @Surya-5555,

Thanks for the review! I've run pre-commit run --all-files locally and pushed all the formatting updates. The code format checks should now pass green.

Let me know if you need anything else!

[Surya-5555]

Hi @Tharun-Varshan-S,
Thanks for cleaning up the PR! The logic and tests look great. Just one quick fix needed:

Issue: In browsergym/webarenalite/src/browsergym/webarenalite/evaluators.py at line 273, except playwright.sync_api.TimeoutError: will raise NameError: name 'playwright' is not defined because playwright isn't imported at module level.

Fix (line 18): Change to from playwright.sync_api import CDPSession, Page, TimeoutError
Fix (line 273): Change to except TimeoutError: pass

[Tharun-Varshan-S]

Hi @Surya-5555,

Thanks for catching that! I have resolved the issue:

• Imported TimeoutError from playwright.sync_api on line 18.
• Updated the exception block to catch TimeoutError directly on line 273.
• Verified formatting via pre-commit.

The fix has been pushed to the branch. Thanks again for the review!