Bump redb 4.0 → 4.1.0

[aram356]

Summary

• Bumps the workspace redb pin from 4.0 to 4.1.0 to track the latest 4.x release.
• Minor bump within the existing major; no API or on-disk format change for the axum adapter's KV store (crates/edgezero-adapter-axum/src/key_value_store.rs).
• Cargo.lock is refreshed (transitive deps re-resolved during the verification run).

Changes

Crate / File	Change
Cargo.toml	redb = "4.0" → redb = "4.1.0"
Cargo.lock	redb 4.0.0 → 4.1.0, plus incidental transitive refresh from cargo check --all-features

Closes

Closes #254

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-targets — full suite green (axum adapter: 102 tests passed, including redb-backed KV contract tests)
• cargo check --workspace --all-targets --features "fastly cloudflare spin"
• cargo check -p edgezero-adapter-spin --target wasm32-wasip1 --features spin

Compatibility notes

• redb 4.1.0 declares MSRV 1.89 — well below the project's pinned 1.91.1.
• 4.0 → 4.1 is a minor bump, no breaking changes; the Drop-impl tightening and Legacy-type removal that landed in 4.0 (and which the codebase doesn't use) are unaffected.
• spin-sdk 5.2 → 6.0 was considered alongside this but deferred — it requires rustc 1.93 and is being tracked separately as a toolchain decision.

Checklist

• Changes follow CLAUDE.md conventions
• No Tokio deps added to core or adapter crates
• No new code (dependency bump only)
• No secrets or credentials committed