#3319 chore: split the compile-check changed-files check file under the line limit

Summary

• No behavior change. Splits fast_path.go so the final pull request into main (#3318) passes CI.

User Impact

• None. The pull request into main failed build-cli, Go CLI Security Analysis, and test-windows-installers on TestProductionGoFilesStayFocused, because fast_path.go had 575 lines against the architecture test's limit of 500 (it counts every line, unlike the SLOC-based file-length check).

Changes

• The baseline record types and the code that records a baseline after a full compile (RecordBaseline, the generator output hashing, baselineFiles, writeBaselineRecord, and the path helpers) move unchanged to baseline_record.go, next to baseline_record_test.go. The check that reads a baseline stays in fast_path.go (now 401 lines).

Verification

• cli/release-automation: go test ./... passes, including TestProductionGoFilesStayFocused, which failed before.
• cli/dispatcher: go vet ./..., golangci-lint fmt --diff, golangci-lint run (0 issues), the complexity config (0 issues), and go test ./... all pass.
• File length check: no file over the limit.