refactor: tsc

[Overtorment]

Note

Add runtime assertions and safer EC ops in UTXO detection and seed derivation, plus a tsc lint script and patch version bump.

• Core (src/index.ts):
  • Add runtime assert checks in seedToCode for bscan/bspend derivation.
  • Refactor EC math in detectOurUtxos and detectOurUtxosUsingTweakbscanBspend by separating tkG computation and asserting results before pointAdd.
  • Define a local assert helper.
  • Minor typing refinement: return Omit<UTXO,'wif'> in detectOurUtxosUsingTweakbscanBspend.
• Build/Meta:
  • Add tslint script (tsc ... --noEmit).
  • Bump version to 2.2.1.

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