ci: shard Go tests and parallelize CDP suite

[pr4bh4sh]

Summary

• Split the Go test suite into four static matrix shards (cdp, s1, s2, s3).
• Keep race detection on the fast shards and run the CDP shard with bounded -parallel 4.
• Mark independent CDP browser tests parallel so they can run concurrently.
• Upload each shard coverage file under the same Codecov flag and report name so Codecov combines them into one report.

Validation

• go test ./... -run '^$'
• go test ./pkg/driver/browser/cdp -parallel 4 -timeout 25m -coverprofile=coverage-cdp.out -covermode=atomic — passed in 3m 06s with 80.9% coverage
• Workflow YAML parsing and matrix package-completeness check
• gofmt and git diff --check

Related tracking issue: pr4bh4sh#9

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[omnarayan]

Thanks @pr4bh4sh, nice work. I approved the workflow run and it's all green:

Job	Time
shard s1	3m 22s
shard cdp	3m 06s
shard s2	2m 37s
shard s3	1m 12s
CI total	3m 44s (was ~8.5–9 min on main)

I also ran the CDP package locally with -parallel 4: it passed in 160s, and none of the tests call newTestDriver twice or use t.Setenv, so the t.Parallel() in the helper is safe.

One request before merging: since the shard package lists are static, could you add a step that fails CI when a package isn't covered by any shard? Otherwise a package added later would silently never be tested. Something like:

go list ./... | sort > all.txt
printf '%s\n' <all shard package lists> | tr ' ' '\n' | sort -u > sharded.txt
diff -u all.txt sharded.txt

A small nit, optional: -parallel "$CDP_PARALLEL" applies to every shard, not only CDP. It's harmless, but a neutral name like TEST_PARALLEL would read better.

Happy to merge once the coverage check is in.