feat(stellar): implement batch sender contract path

[fwseyi]

Summary

• Implement the Stellar stealth batch-sender Soroban contract path.
• Support native XLM and issued-asset transfers.
• Convert payment amounts to stroops and preserve stealth metadata.
• Validate contract configuration, asset consistency, and operation limits.
• Add focused success and regression coverage.

Validation

• pnpm exec vitest run test/chains/stellar/tx-builder.test.ts — 21 passed
• pnpm exec vitest run test/chains/stellar — 909 passed, 5 skipped
• pnpm exec tsc --noEmit — passed
• pnpm build — passed

Closes #199

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[truthixify]

The contract call does not match the deployed ABI. batch_send expects sender, a vector of Transfer structs, and asset, but this PR sends seven separate arguments. Please build the Transfer values and regenerate the API report.

[fwseyi]

The API report conflict has been resolved and the accidental CI setup issue was fixed. The latest CI run is now fully green: all regular checks pass, with only the two expected nightly checks skipped. PR #222 is clean and mergeable.

[truthixify]

The call now has the right three arguments, but each Transfer still includes scheme_id, which is not part of the contract struct. Please encode exactly the four ABI fields and add a contract simulation or round-trip decode test.

[fwseyi]

Thanks for the feedback. I removed scheme_id from the Transfer struct so it now encodes exactly the four ABI fields, and added round-trip decoding assertions to verify the payload shape. The changes are pushed in commit 0bfc38c, and all regular CI checks are passing.

[truthixify]

The transfer fields now match the contract, but the ScMapEntry keys are not sorted. Soroban requires canonical map order. Use nativeToScVal, scvSortedMap, or sort the keys before building the struct.

[fwseyi]

Thanks for catching that. I updated the transfer encoding to use xdr.scvSortedMap() so the ScMapEntry keys are emitted in canonical Soroban order, and updated the round-trip test to verify the exact key order. The fix is pushed in commit 8e20d5f; the focused tests, build, and Stellar API check pass locally. GitHub CI has restarted for the new commit.

[truthixify]

The batch path and tests look good. SDK #227 changed the shared API report, so this now conflicts. Please rebase on develop and regenerate the API report.

[fwseyi]

Rebased PR #222 onto the latest develop, including SDK #227, and resolved the shared API-report conflict. I regenerated and validated the Stellar API report, and the build passes. The rebased changes are now pushed in commit 72fd0fd; CI has restarted.

[truthixify]

Merged. The batch sender call now matches the Soroban ABI, uses canonical map ordering, and passes the focused tests. Thanks @fwseyi.