fix: Throw error if unable to fetch fname server signature

[sanjayprabhu]

Motivation

We're seeing some logs around failing to verify fname server signatures, add logging to track it down.

Change Summary

Describe the changes being made in 1-2 concise sentences.

Merge Checklist

Choose all relevant options below by adding an x now or at any time before submitting for review

• PR title adheres to the conventional commits standard
• PR has a changeset
• PR has been tagged with a change label(s) (i.e. documentation, feature, bugfix, or chore)
• PR does not require changes to the protocol
• All commits have been signed

Additional Context

If this is a relatively large or complex change, provide more details here that will help reviewers

---

PR-Codex overview

Detailed summary

• Fixed a bug where an error was not being thrown if the server address could not be fetched.
• Added a check to throw an error if the signer address is invalid.
• Added a shouldStop flag to stop the provider.
• Added logging and error handling for failed username proof verification.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[changeset-bot]

🦋 Changeset detected

Latest commit: 5bd10a5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@farcaster/hubble	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07 🎉

Comparison is base (1fd9b2b) 70.34% compared to head (e462f16) 70.42%.

❗ Current head e462f16 differs from pull request most recent head 5bd10a5. Consider uploading reports for the commit 5bd10a5 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1120      +/-   ##
==========================================
+ Coverage   70.34%   70.42%   +0.07%     
==========================================
  Files          79       79              
  Lines        7014     7015       +1     
  Branches     1480     1479       -1     
==========================================
+ Hits         4934     4940       +6     
+ Misses       1949     1944       -5     
  Partials      131      131              

Impacted Files	Coverage Δ
apps/hubble/src/eth/fnameRegistryEventsProvider.ts	77.90% <100.00%> (+1.95%)	⬆️

... and 5 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.