chore(release): tighten dependencies, MSRV and feature checks

[wolfv]

Combines the dependency, MSRV and isolated-feature cleanup previously split across #202–204.

• Remove unused dependency declarations and narrow Tokio features.
• Repair TLS feature forwarding.
• Declare and test Rust 1.86 as the workspace MSRV.
• Check each crate with default, no-default and individual features.
• Make native-TLS dependency checks fail closed.

Validation: workspace tests, Rust 1.86 checks, strict Clippy, isolated crate feature checks and cargo-machete passed on the combined stack.

Stack: follows #201; #206 follows this PR.