upgrade: Align Cargo dependencies with wasm-tools 1.243.0 upgrade

Dependabot had suggested bumping wasm crates to 0.242.0, but since we
just upgraded wasm-tools to 1.243.0, align all wasm-tools ecosystem
crates to their matching 0.243.0 versions instead:

tools-builder/toolchains/Cargo.toml:
- wasmparser: 0.240 → 0.243
- wasm-encoder: 0.241 → 0.243
- wat: 1.240 → 1.243
- wit-parser: 0.240 → 0.243
- wit-component: 0.240 → 0.243

tools/wasm_embed_aot/Cargo.toml:
- wasm-encoder: 0.240 → 0.243
- wasmparser: 0.240 → 0.243
- wit-bindgen: 0.46.0 → 0.49.0 (aligns with our wit-bindgen upgrade)

All builds verified - cargo check passes successfully.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: avrabe