Port wasm solver to C and add regression coverage

[Soccera1]

What changed

• Replaced the Rust WASM solver with a C implementation in wasm/src/c/src/cap_wasm.c, including SHA-256 hashing, hex-prefix target parsing, nonce formatting, and wasm allocator shims.
• Removed the old Rust crate under wasm/src/rust and updated the docs/package metadata to describe the solver as C-based WASM.
• Tightened the test suite: wasm/src/c/test-regression.cjs became a fixed regression suite, wasm/test/node.js now asserts expected nonces for the full challenge set, and wasm/test/node_odd_difficulty.js verifies the odd-length target case.
• Updated wasm/build.js so the build runs the regression suite.

Commit breakdown

• 629ed2f: Port wasm from Rust to C
• 978c1f5: Remove Rust code
• dee457e: Update tests

This was done as the rust implementation had many external dependencies, and rustc is very difficult to bootstrap. This version has no external dependencies; it can be compiled with -ffreestanding.
I have also done some unscientific testing and this is over 13% faster.

Summary by CodeRabbit

• New Features

  • Added a full benchmark suite (Node + browser) with runner, browser UI, and an easy local server to compare solver implementations and report speedups.

• Documentation

  • Updated docs and READMEs to describe the client solver as a C-based WebAssembly implementation.

• Tests

  • Added regression tests validating solver correctness across multiple challenge cases.

• Chores

  • Build pipeline updated to produce a C-based WASM solver and related build orchestration.

[Soccera1]

Re-open of #206 since all the commit hashes got fucked, closing branches, thus closing the PR.

[opuadm]

make phone happy

[tiagozip]

did it end up being faster than the current rust one?

[Soccera1]

did it end up being faster than the current rust one?

Only in bun. I'm currently working on resolving this issue.