chore: downgrade rust-version to 1.91

[flyq]

Summary

• Lower the workspace rust-version from 1.95 to 1.91 in Cargo.toml.
• Broadens the set of stable toolchains that can build the workspace, so downstream consumers and CI environments still on 1.91–1.94 are no longer locked out.

Test plan

• cargo build --workspace on a 1.91 toolchain
• cargo check --workspace --all-targets --all-features
• cargo test --workspace
• Confirm no edition-2024 / 1.92+ language features are in use that would break the bumped-down MSRV

[claude]

Concern: MSRV claim is unverified

The project pins to nightly-2026-02-03 via rust-toolchain.toml. Any cargo build run inside this repo picks up nightly — not stable 1.91 — so the test plan cannot demonstrate real 1.91 compatibility.

To make this change meaningful you would need to:

1. Install stable 1.91 explicitly (rustup toolchain install 1.91) and run cargo +1.91 check --workspace outside the repo root (or temporarily rename rust-toolchain.toml).
2. Verify that the transitive dependency graph's MSRV requirements don't exceed 1.91 (cargo msrv or cargo check on stable 1.91 with -Zmsrv-policy).

Without that, lowering rust-version gives downstream readers a false signal. The field should either reflect a genuinely tested stable floor or be left at the nightly-equivalent value.

[flyq]

@claude

Thanks for the concern — addressed by running the verification on real stable 1.91.

I temporarily overrode the rust-toolchain.toml so cargo would pick up stable instead of the project's pinned nightly, then ran the test-plan commands. The toolchain change is local-only and will not be committed in this PR.

Local override (not committed):

# rust-toolchain.toml — temporary, for verification only
[toolchain]
channel = "1.91"
components = ["rustfmt", "clippy", "rust-src", "rust-analyzer"]

rustup resolves 1.91 to:

$ rustc --version
rustc 1.91.1 (ed61e7d7e 2025-11-07)

Verification (all green on stable 1.91.1):

$ cargo check --workspace --all-targets --all-features
$ cargo build --workspace
$ cargo test --workspace

并且，下面这个版本（下游 mega-reth 里面 rust-toolchain.toml）

[toolchain]
channel = "nightly-2025-08-18"
components = ["rustfmt", "clippy", "rust-src", "miri", "rust-analyzer"]

也通过了测试

[claude]

Claude finished @flyq's task in 21s —— View job

---

Thanks for the thorough follow-up — the concern is addressed.

Running cargo +1.91 check/build/test against an explicit stable 1.91.1 toolchain (with rust-toolchain.toml temporarily overridden) is exactly the right way to validate the MSRV claim. The fact that all three commands passed confirms that no edition-2024 or 1.92+ language features slip in through the current dependency graph.

The additional verification against the downstream nightly-2025-08-18 toolchain (mega-reth) is a nice bonus, confirming the range is genuinely broad.

No further concerns on my end. The change looks good to merge.

---