ci(lint): pin ruff and Rust toolchain, fix resulting lint errors

[singlerider]

What

• Pin ruff to 0.16.9 in the lint job and the dev dependency group (uv.lock updated).
• Pin Rust 1.97.1 with clippy and rustfmt in a new rust-toolchain.toml and in rust-tests.yml.
• Fix the 8 ruff errors (import order, __slots__ sort, SIM102, SIM201) and the clippy for_kv_map error in src/node/base.rs.

Why

#92 fails required lint and test checks for reasons outside its diff: unpinned pipx install ruff picked up 0.16.9, and floating stable clippy added for_kv_map. Unblocks #92 for blacklanternsecurity/bbot-enterprise#149.

Validation

Before (on dev):

$ uvx ruff@0.16.9 check
Found 8 errors.
$ cargo clippy --all-targets --all-features -- -D warnings
error: you seem to want to iterate on a map's values
  --> src/node/base.rs:42:27

After:

$ uvx ruff@0.16.9 check
All checks passed!
$ cargo fmt --all -- --check && cargo clippy --all-targets --all-features -- -D warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.55s
$ cargo test --all-features
test result: ok. 72 passed; 0 failed; 2 ignored
test result: ok. 9 passed; 0 failed; 0 ignored
$ uv run pytest -q --disable-warnings .
14 passed in 0.73s

AI-assisted (Jcode).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100%. Comparing base (e26e924) to head (626795f).

Additional details and impacted files

@@         Coverage Diff         @@
##            dev    #94   +/-   ##
===================================
  Coverage   100%   100%           
===================================
  Files         3      3           
  Lines       604    605    +1     
===================================
+ Hits        604    605    +1     

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[singlerider]

Folded into #92.