Publish rainlang-eval + rainlang_test_fixtures to crates.io (unblock raindex's last git deps)

[thedavidmeister]

Context

raindex#2593 wants all git deps removed from raindex — no exceptions. The Rust crates.io cutover is nearly complete: rainlang_bindings, rainlang_dispair, rainlang_parser, the rain-metadata* crates, and rain-math-float are all consumed from crates.io now.

Two crates from this repo are the only remaining git deps in raindex's workspace:

Crate	Why it's still a git dep
rainlang-eval (package = "rainlang-eval")	Depends on foundry-evm via a git dependency, which blocks cargo publish (crates.io rejects git deps).
rainlang_test_fixtures	Marked publish = false. Its only real dep is alloy, so it is otherwise publishable.

Both are currently pinned in raindex at rev 77ffb9f233dbd5daeb522fd4eb22997b2faddab9.

Tasks

• rainlang-eval: remove/replace the foundry-evm git dependency (use a crates.io release, feature-gate it behind a non-default feature, or move the EVM-execution bits to a separate unpublished helper) so the crate can be published.
• rainlang_test_fixtures: drop publish = false and confirm its dependency tree is fully crates.io-resolvable, then publish.
• Publish both to crates.io (via the autopublish Package Release flow).
• In raindex, swap the two git deps in Cargo.toml / crates/test_fixtures/Cargo.toml for the published versions and drop the lib/rain.interpreter rust path references entirely.

Until then, raindex keeps these two as git deps pinned to the rainlang rev matching the published bindings/dispair/parser.