fix: Gracefully handle missing raw button on GitHub file pages

[sentry]

This PR addresses the Error: Raw button not found that occurs when the createCoverageButton function in src/content/github/file/main.tsx cannot find the expected raw button element on a GitHub file page.

Previously, if the raw button was not found (e.g., due to GitHub UI variations, timing issues in SPA navigation, or pages where the button is genuinely absent), the function would throw an error. This error, although handled by Sentry, would cause the entire extension processing for that page to crash, leading to a poor user experience and a high volume of Sentry events.

The fix implements the following changes:

1. createCoverageButton modification: The function now returns undefined instead of throwing an error if the [data-testid="raw-button"] element is not found. The function's return type has been updated to HTMLElement | undefined.
2. main() guard clause: A check has been added in the main() function. If createCoverageButton() returns undefined (meaning the raw button was not found), the main() function will now gracefully exit early, preventing further processing and avoiding any crashes.

This change ensures that the extension remains robust and does not crash on pages where the raw button is not present, while still functioning as expected on pages where it is available.

Fixes BROWSER-EXTENSION-1Q

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[codecov]

Bundle Report

Changes will increase total bundle size by 84 bytes (0.01%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
codecov-browser-extension-array-push	660.55kB	84 bytes (0.01%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: codecov-browser-extension-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
background.js	89 bytes	207.75kB	0.04%
githubFile.js	-5 bytes	11.46kB	-0.04%

Files in githubFile.js:

• ./src/content/github/file/main.tsx → Total Size: 11.79kB