fix: Handle missing GitHub raw button gracefully

[sentry]

This PR addresses the "Error: Raw button not found" issue (BROWSER-EXTENSION-SA) which occurred when the extension attempted to locate GitHub's [data-testid="raw-button"] element.

Root Cause:
The error stemmed from the extension querying for the 'Raw' button immediately upon page load or soft-nav:end events. This often happened before GitHub's DOM was fully rendered, or in cases where the button might legitimately be absent (e.g., for certain file types or GitHub UI variations). The previous implementation would throw an error if the element was not found instantly.

Solution:

1. waitForElement Utility: Introduced a new asynchronous utility function waitForElement in src/content/github/file/utils/waitForElement.ts. This utility uses a MutationObserver to efficiently wait for a specified DOM element to appear within a given timeout, resolving with the element or rejecting with a custom ElementNotFoundError.
2. Graceful Element Retrieval: Replaced the synchronous document.querySelector calls with await waitForElement in createCoverageButton() (main.tsx) and createDropdown() (dropdown.tsx).
3. Typed Error Handling: Created a custom ElementNotFoundError class to provide specific error identification.
4. Error Suppression: Updated the try/catch block in main.tsx and added .catch() handlers to the createDropdown calls. These now specifically check for ElementNotFoundError and, if caught, log a message to the console and return early without reporting to Sentry. This prevents unnecessary error reports for expected scenarios where the 'Raw' button might not be present or takes longer to render.

Fixes BROWSER-EXTENSION-SA

_{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 774 bytes (0.12%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
codecov-browser-extension-array-push	661.24kB	774 bytes (0.12%) ⬆️

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	685 bytes	12.15kB	5.98% ⚠️

Files in githubFile.js:

• ./src/content/github/file/utils/dropdown.tsx → Total Size: 1.91kB

• ./src/content/github/file/main.tsx → Total Size: 12.56kB

• ./src/content/github/file/utils/waitForElement.ts → Total Size: 1.33kB