Cap proxy protocol TLV vector entry counts

[parasol-aser]

Summary

• cap each proxy protocol TLV vector at 64 entries, including SSL sub-TLV vectors
• reject overly dense TLV payloads before they can grow per-connection allocations on the proxy unix-socket path
• add parser tests for the boundary, over-limit top-level TLVs, and over-limit SSL sub-TLVs

Testing

• bazel test //src/mongo/transport:transport_test --test_arg=--gtest_filter=ProxyProtocolHeaderParser.*

[kelly-cs]

Hi @parasol-aser!

Thanks for making this pull request! We just need a couple of things from you to start our consideration of the PR. Can you please:

1. Sign our Contributor's Agreement.

2. Create a new SERVER ticket on JIRA.