docs: add comprehensive JSDoc documentation to utility functions and error classes

[Dark-Brain07]

Description

This PR adds comprehensive JSDoc documentation to exported utility functions in utils.ts and all error classes in errors.ts within the @stacks/transactions package.

Changes

packages/transactions/src/utils.ts

• Added JSDoc with @param, @returns, and @example tags to:
  • leftPadHex
  • leftPadHexToLength
  • rightPadHexToLength
  • exceedsMaxLengthBytes
  • hash160
  • isClarityName
  • validateStacksAddress

packages/transactions/src/errors.ts

• Added JSDoc documentation with usage examples to all error classes:
  • TransactionError (base class)
  • SerializationError
  • DeserializationError
  • NoEstimateAvailableError
  • NotImplementedError
  • SigningError
  • VerificationError

Motivation

These utility functions and error classes are widely used across the Stacks ecosystem but lacked inline documentation. Adding JSDoc improves:

• IDE experience — developers get instant hover documentation and parameter hints
• Onboarding — new contributors can understand function behavior without reading source code
• API reference generation — JSDoc tags enable automated documentation tools

Testing

Documentation-only changes. No functional code was modified.