build(deps): update cap-std to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
cap-fs-ext	dependencies	major	3 → 4
cap-std	dependencies	major	3 → 4

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Release Notes

bytecodealliance/cap-std (cap-fs-ext)

v4.0.0

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[github-actions]

🌐 Demo preview: https://renovate-cap-std.eryx-bvy.pages.dev
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[sd2k]

Triage: blocked upstream, no fix pushed.

`eryx-vfs` gets `read_at`/`write_at` on `Arc<cap_std::fs::File>` from `system_interface::fs::FileIoExt` (crates/eryx-vfs/src/streams.rs), enabled via the `cap_std_impls` feature of `system-interface = "0.27"`. Those impls are written against cap-std 3, so bumping cap-std to 4 on its own breaks them:

error[E0599]: no method named `read_at` found for struct `Arc<cap_std::fs::File>` in the current scope
error[E0599]: no method named `write_at` found for struct `Arc<cap_std::fs::File>` in the current scope
error: could not compile `eryx-vfs` (lib) due to 5 previous errors

The blocker is that no published system-interface supports cap-std 4 — the latest (0.27.3) still declares cap-std ^3.0.0 (and cap-fs-ext ^3.0.0, cap-tempfile ^3.0.0). So there is no version pairing that makes this compile today.

Options, both of which are judgement calls rather than dependency bumps:

1. Hold this PR until system-interface releases cap-std 4 support.
2. Drop the FileIoExt dependency for these two operations and implement positional read/write directly against the underlying fd (std::os::unix::fs::FileExt, plus a Windows equivalent — streams.rs is used on the Windows CI target too).

Note this is the same wall #207 ("bump cap-std from 3 to 4") has been sitting behind since May; that PR only bumps the manifest and never addressed the FileIoExt impls.

Also worth noting for renovate.json5: system-interface belongs in the cap-std lockstep group. It is currently ungrouped, so Renovate can propose a cap-std major on its own — exactly what happened here.

Automated dependency triage. No changes pushed to this branch.

[sd2k]

Superseded by #327 — cap-std bumping alone is unbuildable until system-interface releases cap-std v4 support (its cap_std_impls feature is version-locked to a cap-std major). The "cap-std" Renovate group now holds cap-std + system-interface together and will reopen this combination once upstream is ready. Closing in favor of that grouped PR.

[renovate]

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