feat(wallet): add SigmaJS prover

[TerraTectra]

Summary

• add a SigmaJS-backed ISigmaProver implementation to @fleet-sdk/wallet
• reduce and sign transactions protected by arbitrary ErgoTree scripts
• support Fleet and EIP-12 unsigned transaction objects, explicit token burning, network and base-cost options
• sign and verify Sigma proposition message proofs through SigmaJS
• add documentation, package dependency and release changeset

Validation

• pnpm test:unit — 67 files, 1,142 tests passed
• pnpm cov:check — 100% statements, functions and lines; new prover has 100% branch coverage
• pnpm test:lint — passed
• pnpm -r build — passed
• pnpm --filter @fleet-sdk/wallet build — passed without warnings

Closes #110

[changeset-bot]

🦋 Changeset detected

Latest commit: 4310ceb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@fleet-sdk/wallet	Minor
@fleet-sdk/mock-chain	Minor

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[ArgosOff]

@arobsn @mhrn83 could you please review this submission for issue #110 and confirm the 50 ERG bounty status? The PR is currently mergeable. It adds the SigmaJS prover, transaction and message signing tests, documentation, and a changeset. I am available to address review feedback promptly here in writing.

[ArgosOff]

Local verification update: branch is 0 commits behind master and mergeable. Recursive workspace build passes, exit 0. Lint passes across 218 files and format/import checks pass across 220 files. New SigmaJS prover tests pass 10/10. Targeted V8 coverage for sigmaJsProver.ts is 100% statements, branches, functions, and lines. Full unit run reached 1141/1142; the only failure was the unchanged property test in proveDLogProtocol.spec.ts timing out at 5 seconds under full-suite load. Its immediate isolated rerun passed 8/8 in 3.82 seconds, including the timed-out test in 2.56 seconds. No file involved in that transient timeout is modified by this PR. Ready for review.

[TerraTectra]

Hi @arobsn тАФ following up on the SigmaJS prover submitted for #110. As of September 5, this PR remains open and mergeable, with no maintainer review recorded. Before putting more work into it, could you confirm whether the implementation is still wanted and whether the advertised 50 ERG bounty is still funded? If it is, please identify the remaining acceptance requirements and the payout process following acceptance. A short тАЬstill wanted / no longer neededтАЭ reply would also help us close the loop. No additional scope is assumed.