chore: bump MSRV and toolchain to 1.96

[worktrunk-bot]

Summary

Weekly toolchain maintenance: bump MSRV and the development toolchain to latest stable − 1. Current stable is Rust 1.97.0 (2026-07-07), so both move 1.95 → 1.96.

Files updated:

File	Field	1.95 → 1.96
Cargo.toml	rust-version	✅
tests/helpers/wt-perf/Cargo.toml	rust-version	✅
rust-toolchain.toml	channel	1.95.0 → 1.96.0

flake.lock

Not refreshed this run. flake.nix reads the channel from rust-toolchain.toml, so the locked rust-overlay revision only needs to know about 1.96.0. The current pin (oxalica/rust-overlay@4a408e1, lastModified ≈ 2026-06-01) postdates Rust 1.96.0's release (≈ 2026-05-26, the stable before 1.97.0), so it already carries the 1.96.0 manifest and the flake evaluates without a lock bump.

I could not run nix flake update to bump the revision anyway: nix isn't installed in this CI sandbox and the Determinate installer needs root, which isn't available here (no passwordless sudo). If a maintainer prefers to also advance rust-overlay to its latest revision, nix flake update locally will do it — but it's not required for this bump.

Verification

No Rust toolchain is available in this sandbox (cargo/rustc/rustup absent), so cargo msrv verify and cargo run -- hook pre-merge --yes were not run locally. CI's matrix (which installs 1.96.0 via rust-toolchain.toml) and the cargo-msrv job are the verification backstop — please confirm they go green before merge.

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🤖 Weekly toolchain maintenance