[rust] Improve SM error messages when browser/driver version not found

[AutomatedTester]

Summary

Closes #17555

When Selenium Manager cannot resolve a requested browser or driver version, the previous error messages were generic and gave users no guidance on where to find valid versions. This PR adds per-browser links to canonical version lists in all relevant error paths.

Changes per browser/driver:

• Chrome / chromedriver: Link to https://googlechromelabs.github.io/chrome-for-testing/ (already a constant CFT_URL)
• Firefox (browser): Link to https://www.mozilla.org/en-US/firefox/releases/
• geckodriver: Link to https://github.com/mozilla/geckodriver/releases/ (already a constant DRIVER_URL)
• Edge: Link to https://developer.microsoft.com/microsoft-edge/webdriver/
• IEDriverServer: Link to https://github.com/SeleniumHQ/selenium/releases/ (already a constant DRIVER_URL)

Example before:

chrome 999.0 not available for download
Unable to discover firefox 999 in online repository

Example after:

chrome 999.0 not available for download. Check available versions at https://googlechromelabs.github.io/chrome-for-testing/
Unable to discover firefox 999 in online repository. Check available versions at https://www.mozilla.org/en-US/firefox/releases/

Implementation approach:

• Added get_browser_versions_url() default trait method (returns "") to SeleniumManager
• Each browser manager overrides it with its canonical URL
• throw_error_message() appends the URL when non-empty (used by unavailable_download() and unavailable_discovery())
• download_browser() in lib.rs also appends the URL to the minimum-version error
• geckodriver and IEDriverServer "not found" errors updated directly since they don't go through throw_error_message

Test plan

• //rust:unit passes
• 17/19 integration tests pass; 2 failures (integration_browser_download_tests_test, integration_stable_browser_tests_test) are pre-existing network-dependent download tests unrelated to this change