[sunred-liu]

closes #913
closes #915

Summary

Two related TypeScript improvements to the SDK.

1. parseContractError — contract error codes → typed errors (#913)

Soroban host errors surface as raw integers (e.g. Error(Contract, #12)), so
callers get no actionable message and cannot branch on the failure reason.

parseContractError(error, contract?, context?) extracts the numeric contract
error code from an unknown value and maps it to the matching typed error class:

Contract error	Mapped to
stream #11 ClawbackDisabled	ClawbackNotEnabledError
stream #1 NotAuthorized	UnauthorizedStreamActionError (with operation + caller)
stream #2 StreamNotFound	StreamNotFoundError (with streamId)
stream lifecycle codes	InvalidStreamStateError (with operation)
factory #8 / #9 / #6	RateExceedsMaxError / DurationTooShortError / BackdatedStreamError
governor #2 InvalidParam	GovernorInvalidParamError
any other known code	ConduitError with the contract-scoped message

Design notes:

• Error numbers are contract-scoped. The same numeric code means different
  things on the stream, factory and governor contracts, so the contract
  argument selects the catalogue to read. When it is omitted the code is
  auto-resolved only if exactly one contract defines it; otherwise a
  ContractError lists the candidates rather than reporting the wrong meaning.
• No invented values. The richer stream errors carry a stream ID, an
  operation and a caller that cannot be recovered from the numeric code. They
  are only built when the caller supplies that context; otherwise a
  ConduitError with the correct message is returned.
• Safe in a catch block. Errors without a contract error code (network
  failures, timeouts, user cancellations) are returned unchanged.

2. Typed batch payloads (#915)

Batch operations accepted loosely-shaped objects. Two dedicated payload types
now make the required fields explicit:

• BatchStreamCreationPayload — requires recipient, token and
  depositAmount, so a missing recipient or a misformatted amount is a
  compile-time error.
• BatchWithdrawPayload — requires streamId.

StreamsModule.createBatchStreams() and StreamsModule.batchWithdraw() use
the new types. The existing StreamConfig and BatchWithdrawItem names stay
as compatible aliases, so this is not a breaking change.

Verification

• npx tsc --noEmit — no new type errors (the 12 pre-existing errors in
  client.ts / custom-fetch.ts / soroban.ts are unchanged from main).
• npx vitest run — 18 new tests added (14 for parseContractError, 4 for
  the payload types), all passing. The 17 failing tests in
  custom-fetch* / relayer-stress / soroban-retry-after /
  streams.test.ts fail identically on main and are unrelated to this
  change.