feat: add retry logic for logins

[aiell0]

Summary

• add retry support around buf registry login so transient BSR slowness does not fail the action immediately
• introduce login_retries and login_retry_delay_seconds action inputs with defaults of 5 retries and 10 seconds between attempts
• validate retry inputs, document the new behavior in the README, and rebuild the bundled dist/ artifacts

Why

BSR login currently fails on the first slow or temporary registry response. This change makes login more resilient in CI while still allowing users to tune retry behavior when they need different timing.

Error

Run bufbuild/buf-action@v1
Using the latest release of buf: 1.68.4
Downloading buf (1.68.4)
Setup buf (1.68.4) at /home/runner/_work/_tool/buf/1.68.4/x64
/home/runner/_work/_tool/buf/1.68.4/x64/buf registry login rogo.buf.dev --token-stdin
Failure: the server hosted at that remote is unavailable.
Error: The process '/home/runner/_work/_tool/buf/1.68.4/x64/buf' failed with exit code 1

Testing

• npm ci
• npm run lint
• npm run build

[CLAassistant]

All committers have signed the CLA.

[emcfarlane]

Thanks for the PR. It would be good to correlate these failures with logs on our side before deciding if this is the right approach. If its a LB blip I think we can get away with a more conservative retry approach and apply it to more methods. I'm not sure if this is the right place.