transport: Prevent sending negative timeouts

[arjan-bal]

After #8290 is merged, negative timeout values fail the request with an internal status instead of a deadline exceeded. This test uses negative deadlines and can fail if the server sends an internal error before the client sees the deadline expire.

Sample failure: https://github.com/grpc/grpc-go/actions/runs/14979137997/job/42078795928?pr=8308

The client checks the deadline expiry before creating a stream.

grpc-go/stream.go

Lines 410 to 413 in 709023d

	func (cs *clientStream) newAttemptLocked(isTransparent bool) (*csAttempt, error) {
	if err := cs.ctx.Err(); err != nil {
	return nil, toRPCErr(err)
	}

However, the deadline may expire after this check, but before the grpc-timeout header is created.

RELEASE NOTES:

• transport: Fail RPCs on the client when using extremely short contexts that expire before the grpc-timeout header is created.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.22%. Comparing base (d36b02e) to head (e1bcc17).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8312      +/-   ##
==========================================
+ Coverage   82.19%   82.22%   +0.03%     
==========================================
  Files         419      419              
  Lines       41992    41992              
==========================================
+ Hits        34516    34530      +14     
+ Misses       6008     5997      -11     
+ Partials     1468     1465       -3     

Files with missing lines	Coverage Δ
internal/transport/http2_client.go	92.15% <100.00%> (-0.52%)	⬇️

... and 18 files with indirect coverage changes

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[dfawley]

This is even worrysome. If it takes >1ms before the timeout is computed by grpc, then it could fail. It seems like there's probably something in our code that we should change that prevents the client from sending a negative deadline instead.

[arjan-bal]

Made the fix to validate the timeout on the client side and return a DeadlineExceeded error.

[dfawley]

Nice, thank you for fixing this!

[dfawley]

This should say what it's doing in the error message, to make debugging a failure easier.