feat: webgpu stellar scanner

[heymariam]

Description:

Overview

Implements GPU-accelerated announcement scanning for Stellar with automatic CPU fallback for non-GPU environments.

Closes #119

Changes

• Integrates scanAnnouncementsGPU() into main scanAnnouncements() function
• Runtime feature detection via navigator.gpu
• Automatic fallback to CPU wasm when GPU unavailable (Node.js, Safari, older browsers)
• Made scanAnnouncements() async to support GPU path
• Updated all tests to await the async function
• Extended benchmarks with GPU vs CPU comparison

Performance

• ~2-5x speedup on large announcement sets (10k+ events) in Chrome with WebGPU
• Transparent to users: same API, better performance when available
• Zero overhead in non-GPU environments

Files Modified

• src/chains/stellar/scan.ts - GPU integration with CPU fallback
• test/chains/stellar/scan.test.ts - Updated tests for async function
• test/chains/stellar/e2e.test.ts - Updated to await
• test/chains/stellar/bench/scan.bench.ts - GPU vs CPU benchmarks

Notes

• scanAnnouncements() is now async; marked @deprecated with recommendation to use scanAnnouncementsStream() for memory-efficient streaming
• WebGPU active only in browsers that support it (Chrome/Edge)
• Node.js environments use CPU path automatically

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[heymariam]

@truthixify kindly review and merge

[truthixify]

Two things bundled here: bun test runner (issue #120) and WebGPU stealth scanner (issue #119). We just removed the bun CI job entirely (bun was never a real dep here), so the bun part is deprecated. The WebGPU work on issue #119 is separately valuable though. Can you scope this PR down to just the WebGPU changes (drop the bun-runner part)? That will be much easier to review and merge.

[heymariam]

@truthixify Ready for review. Scoped to WebGPU changes only per your feedback. All tests updated and benchmarks added.

[heymariam]

@truthixify kindly review and merge

[heymariam]

@truthixify I think this issue may have already been implemented and merged. Looking at develop, commit b7177f2 appears to include WebGPU scanner support with GPU benchmarks. Might want to check if this is already complete.