Add WASM support

[alexvbrdn]

What this changes

This PR introduces comprehensive support for the wasm32-unknown-unknown target and resolves a shuffling limitation on 32-bit architectures.

WASM Support & Fixes:

• ahash without getrandom: On wasm32-unknown-unknown, ahash now uses the compile-time-rng feature. This drops the getrandom dependency (which requires a backend opt-in on WASM), allowing the crate to build out-of-the-box. (Closes make ahash optional #17)
• Removed rayon on WASM: Since WASM lacks native threads, rayon only ran its single-thread fallback. It is no longer a dependency on WASM targets. FastAutomaton::union_all_par and FastAutomaton::intersection_all_par are excluded on WASM, while keeping the parallel feature harmless if enabled by another crate in the dependency graph.
• Customizable Execution Clock: Added ExecutionProfileBuilder::clock, ExecutionProfile::with_clock, and execution_profile::Clock. This allows WASM hosts to supply their own monotonic clock (e.g., performance.now()) to prevent timeouts from panicking on Instant::now, while also enabling fully deterministic timeout testing across all targets.

32-bit Fix:

• 64-bit Shuffling Window: Fixed a bug on 32-bit targets (wasm32, i686, armv7, etc.) where CharacterOrder::Shuffled and PathOrder::Shuffled were restricted to 2^32 combinations due to usize indexing. The window is now strictly 64-bit on all targets.

Checklist

• cargo fmt --all --check and cargo clippy --all-targets -- -D warnings pass
• cargo test and cargo test --no-default-features pass
• New public items are documented
• A test covers the change
• CHANGELOG.md is updated under ## [Unreleased]
• The change builds on Rust 1.88, or the MSRV bump is intentional and noted