Do not allow relays to have point-at-infinity pubkey

[jtraglia]

📝 Summary

• Return an error if a relay is configured with the point-at-infinity (all-zero) pubkey.
• Delete blank lines in test cases (just a nit picky thing I want to fix).
• Rename a test case for consistency:
  • From: "Invalid relay public key"
  • To: "Relay URL with invalid public key"

⛱ Motivation and Context

@asanso pointed out that if a relay were configured with the point-at-infinity public key, it could essentially bypass signature verification checks when receiving bids. In practice, this isn't a problem. A user would need to configure mev-boost with this and there's already a trusted relationship with relays (i.e., we trust them to only send valid bids/payloads). But I do think it's a good situation to avoid and that's why I'm making this PR.

---

✅ I have run these commands

• make lint
• make test-race
• go mod tidy

[ralexstokes]

generally looks good, I like reducing attack surface here, even though I agree this is a bit minor

[codecov-commenter]

Codecov Report

Merging #493 (27b0411) into main (7735b00) will increase coverage by 0.14%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #493      +/-   ##
==========================================
+ Coverage   68.64%   68.79%   +0.14%     
==========================================
  Files           8        8              
  Lines        1263     1269       +6     
==========================================
+ Hits          867      873       +6     
  Misses        346      346              
  Partials       50       50              

Flag	Coverage Δ
unittests	68.79% <100.00%> (+0.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/relay_entry.go	90.00% <100.00%> (+2.50%)	⬆️

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[metachris]

thanks!