feat(streams): WASM plugin support for Rust Arroyo adapter

[fpacifici]

Summary

• Add a WasmProcessor pipeline step (bytes → bytes) that loads a WASM component from module_path and wires it into the Rust Arroyo adapter.
• Define the guest contract in WIT (sentry_streams/wit/processor.wit): submit, submit_watermark, and poll returning messages or watermarks. Host provides a log import; WASI Preview 2 is linked at runtime (not in the WIT file).
• Implement a single-threaded WasmProcessor Arroyo strategy using wasmtime (one Store + guest instance per step).
• Add a componentize-py example guest under examples/wasm_guest/ and a minimal Rust passthrough guest for unit tests (tests/fixtures/wasm_passthrough.wasm).

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