refactor(conformance): reduce cognitive complexity in sdk dispatcher (#82)

* refactor(conformance): reduce cognitive complexity in sdk dispatcher

Extract 30+ sub-handler functions into sdkHelpers.ts to bring all 8
S3776 violations (max complexity 71) below the 15-allowed threshold.
Removes dead StorageUtils import and redundant odd-hex padding.
6601 conformance vectors continue to pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* refactor(conformance): drive remaining S3776 below threshold in sdkHelpers

Extract helpers to bring functions at L195 (CC 19) and L696 (CC 21) under
the cognitive-complexity limit of 15.

- merklePathFromBump (CC 19) → split into assertMerklePathStructure,
  assertTxidMerkleRoots, assertSparseTxidRoots; public function now CC 2
- dispatchNodeTransactionFixture (CC 21) → split into
  parseTransactionOrReturnInvalid, countRejectedSpends, countOneSpend;
  public function now CC 3

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* chore(sonar): remove unused ECDSA and decodeMessage imports

ECDSA usage moved to sdkHelpers.ts during the L195/L696 refactor (commit
1b04e0e); the import in sdk.ts is now dead. decodeMessage is exported
from sdk.ts but never consumed by sdkHelpers.ts.

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sirdeggen