feat(wal): add crash-safe write-ahead log package

[derekbit]

Which issue(s) this PR fixes:

Issue longhorn/longhorn#13259

What this PR does / why we need it:

Append-only WAL with binary framing (magic+ver+type+len+CRC32C), fdatasync-per-record durability, gofrs/flock cross-process exclusion, torn-tail truncation on Open, RecTxnPrepare gate for atomic intent-set durability, and OpenWithQuarantine for unreadable-file fallback.

Designed to support snapshot-chain transactional recovery for the longhorn-engine replica, but the package is generic.

Special notes for your reviewer:

Additional documentation or context

[Copilot]

Pull request overview

This PR introduces a new wal package providing a crash-safe, append-only write-ahead log intended to support snapshot-chain transactional recovery workflows (e.g., longhorn-engine replica directory operations), with per-record sync durability, torn-tail detection/truncation, and cross-process exclusion via file locking.

Changes:

• Added wal journal implementation with binary framing + CRC32C validation, scanning utilities, and quarantine-on-open fallback.
• Added recovery analysis (Analyze) to derive pending transactions/intents/step status from scanned records.
• Updated dependencies (notably gofrs/flock) and vendored modules; bumped testify and updated x/exp.

Reviewed changes

Copilot reviewed 7 out of 31 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
wal/types.go	Defines WAL operation/action enums and stable on-disk record/payload types.
wal/testing.go	Adds a testing-only helper to simulate abrupt journal shutdown without checkpointing.
wal/recovery.go	Implements journal record analysis to identify pending/incomplete transactions for recovery.
wal/recovery_test.go	Adds unit tests for recovery analysis behavior and error cases.
wal/journal.go	Implements the WAL journal (framing, CRC, torn-tail truncation, locking, scan, checkpoint, quarantine open).
wal/journal_test.go	Adds end-to-end tests for journal behavior (round-trip, torn tail, CRC truncation, flock exclusion, ScanFile, quarantine).
go.mod	Adds github.com/gofrs/flock and bumps testify / updates x/exp.
go.sum	Updates checksums for new/updated dependencies.
vendor/modules.txt	Records vendored module versions (adds gofrs/flock, updates testify, updates x/exp).
vendor/github.com/stretchr/testify/assert/yaml/yaml_fail.go	Vendored testify update (build tag/header changes).
vendor/github.com/stretchr/testify/assert/yaml/yaml_default.go	Vendored testify update (build tag/header changes).
vendor/github.com/stretchr/testify/assert/yaml/yaml_custom.go	Vendored testify update (build tag/header changes).
vendor/github.com/stretchr/testify/assert/http_assertions.go	Vendored testify update (error message formatting improvements).
vendor/github.com/stretchr/testify/assert/doc.go	Vendored testify update (documentation note).
vendor/github.com/stretchr/testify/assert/assertions.go	Vendored testify update (caller info, Empty semantics, error-chain formatting, etc.).
vendor/github.com/stretchr/testify/assert/assertion_order.go	Vendored testify update (type formatting in failure messages).
vendor/github.com/stretchr/testify/assert/assertion_forward.go	Vendored testify update (forwarders/docs for new semantics/APIs).
vendor/github.com/stretchr/testify/assert/assertion_format.go	Vendored testify update (formatted assertion helpers/docs).
vendor/github.com/stretchr/testify/assert/assertion_compare.go	Vendored testify update (preformatted failure messages; type formatting).
vendor/github.com/gofrs/flock/SECURITY.md	Adds vendored gofrs/flock security policy documentation.
vendor/github.com/gofrs/flock/README.md	Adds vendored gofrs/flock README.
vendor/github.com/gofrs/flock/Makefile	Adds vendored gofrs/flock build/test targets.
vendor/github.com/gofrs/flock/LICENSE	Adds vendored gofrs/flock license.
vendor/github.com/gofrs/flock/flock.go	Adds vendored gofrs/flock core implementation.
vendor/github.com/gofrs/flock/flock_windows.go	Adds vendored gofrs/flock Windows locking implementation.
vendor/github.com/gofrs/flock/flock_unix.go	Adds vendored gofrs/flock Unix flock-based implementation.
vendor/github.com/gofrs/flock/flock_unix_fcntl.go	Adds vendored gofrs/flock fcntl-based implementation for specific Unix platforms.
vendor/github.com/gofrs/flock/flock_others.go	Adds vendored gofrs/flock stub implementation for unsupported platforms.
vendor/github.com/gofrs/flock/build.sh	Adds vendored gofrs/flock cross-platform build script.
vendor/github.com/gofrs/flock/.golangci.yml	Adds vendored gofrs/flock linter configuration.
vendor/github.com/gofrs/flock/.gitignore	Adds vendored gofrs/flock gitignore.

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[codecov]

Codecov Report

❌ Patch coverage is 69.09091% with 136 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.30%. Comparing base (02405f5) to head (9a66791).

Files with missing lines	Patch %	Lines
wal/journal.go	66.86%	68 Missing and 44 partials ⚠️
wal/recovery.go	74.28%	12 Missing and 6 partials ⚠️
wal/testing.go	57.14%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
- Coverage   74.51%   73.30%   -1.22%     
==========================================
  Files          42       46       +4     
  Lines        2017     2457     +440     
==========================================
+ Hits         1503     1801     +298     
- Misses        369      452      +83     
- Partials      145      204      +59     

Flag	Coverage Δ
unittests	73.30% <69.09%> (-1.22%)	⬇️

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