chore: use protovalidate interceptor instead of protoc-gen-validate interceptor

[tstirrat15]

Description

Development on protoc-gen-validate has basically stopped in favor of protovalidate. It's intended to be a more consistent and flexible validation framework.

This does mean that it will be slightly slower, but not slower enough to be meaningful: https://bufbuild.slack.com/archives/CRZ680FUH/p1760037391133719?thread_ts=1759933966.935909&cid=CRZ680FUH

Changes

• Use protovalidate middleware

Testing

Review. See that validation still happens as expected.

[codecov]

Codecov Report

❌ Patch coverage is 86.36364% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.92%. Comparing base (15ae719) to head (5cffb98).

Files with missing lines	Patch %	Lines
pkg/genutil/protovalidate.go	50.00%	2 Missing and 1 partial ⚠️

❌ Your project check has failed because the head coverage (32.92%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (15ae719) and HEAD (5cffb98). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (15ae719)	HEAD (5cffb98)
	24	20

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2863       +/-   ##
===========================================
- Coverage   74.51%   32.92%   -41.59%     
===========================================
  Files         489      423       -66     
  Lines       60361    54306     -6055     
===========================================
- Hits        44973    17875    -27098     
- Misses      12235    34598    +22363     
+ Partials     3153     1833     -1320     

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[miparnisari]

please run a couple of manual tests to ensure that the validation still works as expected (docker-compose up --build for example). Try both HTTP and gRPC endpoints

i'm also wary of the handwrittenvalidation below. i don't know what it does but i'd want to make sure we didn't accidentally break it