Adopt camino/cap-std path types across the integration test suite

[lodyai]

Context

During the review of #415 (broaden the static-regex lint guard, closes #410), CodeRabbit suggested migrating the new tests/static_regex_lint.rs from std::path/std::fs to camino path types and cap_std::fs_utf8 APIs.

This was deferred from that PR because doing it for one new test file in isolation would:

• add two dependencies (camino, cap-std) that are currently absent from the tree (Cargo.lock has zero references), and
• diverge from the rest of the integration suite, which consistently uses std::fs/std::path and tempfile (for example tests/cli.rs),

so it fell outside the minimal-change scope of the lint fix.

Proposal

If UTF-8 path guarantees and capability-scoped filesystem access are desired, adopt them suite-wide rather than piecemeal:

• Add camino and cap-std as dev-dependencies.
• Migrate the integration tests under tests/ from std::path::{Path, PathBuf} to camino::{Utf8Path, Utf8PathBuf}.
• Replace ad hoc std::fs calls with cap_std::fs_utf8 equivalents, preserving existing Command execution and TempDir handling.
• Establish the convention (e.g. in the developers guide) so new tests follow it.

Please import the latest whitaker user's guide from https://raw.githubusercontent.com/leynos/whitaker/refs/heads/main/docs/users-guide.md as docs/whitaker-users-guide.md which covers the new whitaker functionality allowing suppression of the no_std_fs lint at the path level.

Acceptance criteria

• camino/cap-std added as dev-dependencies with a rationale recorded.
• Integration tests use Utf8Path/Utf8PathBuf and cap_std::fs_utf8 consistently, with no behavioural regressions.
• The convention is documented so the suite stays consistent.

References

• Originating PR: Broaden static-regex lint guard to cover supported lazy wrappers (#410) #415
• Originating issue: Broaden static-regex lint guard to cover supported lazy wrappers #410

[coderabbitai]

🔗 Related PRs

leynos/netsuke#410 - Adopt the Whitaker Dylint suite in the lint gate and CI [merged]
leynos/netsuke#414 - Enumerate tracked Cargo manifests in the Dependabot hygiene test (#413) [merged]
leynos/netsuke#448 - Remove ambient fs [merged]
leynos/whitaker#315 - Add module-path suppression to no_std_fs_operations [merged]
leynos/netsuke#468 - Rename internal canonicalize identifiers (#408) [merged]

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