Fix double spend bug

[dewabisma]

Summary

• Add early guard on confirmSend
• Only send the same extrinsic without creating new one that cause nonce to be incremented
• Remove excessive looping on app level, only rely on SDK level

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Note

High Risk
Changes core transaction submission and nonce handling for all sends; incorrect retry or hash logic could still drop or mis-track in-flight transfers.

Overview
Fixes a double-spend risk where app-level submission retries re-ran the builder and signed new extrinsics (incrementing nonce) while an earlier attempt might already be in the pool.

Mobile: TransactionSubmissionService drops maxRetries and the recursive retry loop in _submitAndTrackBackground; each user action triggers a single submissionBuilder() call, with RPC resilience documented as living in SubstrateService.submitExtrinsic. Review send adds an early if (_submitting) return on confirm to block duplicate taps.

SDK: submitExtrinsic now builds and signs the payload once, then retries broadcasting the same signed bytes. New extrinsic_submission_utils treats Substrate 1013 / already imported as success by returning localExtrinsicHash(extrinsic) so tracking can continue without re-signing. Unit tests cover the helpers.

^{Reviewed by Cursor Bugbot for commit f4eba5f. Configure here.}

[n13]

Same as #515