Move benchmark-only deps behind build tag

[fanyang89]

Motivation

• Reduce unnecessary runtime build dependencies because leveldb, wal, and lz4 are only used by benchmarks and gookit/color overlaps with pterm utilities.
• Make normal go test / build faster and avoid pulling heavy benchmark-only modules during normal development.

Description

• Split VFS raw benchmark code into a new file cmd_vfs_raw_bench_test.go guarded by //go:build benchmark so benchmark-only imports are only required for benchmark builds.
• Trimmed cmd_vfs_raw_test.go to keep only unit tests and removed benchmark helpers from that file.
• Replaced direct usage of github.com/gookit/color in pterm_writer.go with pterm.RemoveColorFromString to rely on pterm utilities instead of an extra color dependency.
• Removed benchmark-only direct requirements (github.com/pierrec/lz4/v4, github.com/syndtr/goleveldb, github.com/tidwall/wal, and github.com/gookit/color) from the main require block and cleaned corresponding entries from go.sum.

Testing

• Ran gofmt on modified files successfully to normalize formatting and committed the changes.
• Attempted go mod tidy, which could not complete fetching some modules due to proxy/network restrictions (module fetch errors for benchmark-only modules), so dependency verification for those modules was not completed.
• No unit/benchmark test runs were executed as part of this change in the current environment.

---

Codex Task