refactor(bitcoin_client_js): migrate descriptors to v3 and upgrade bitcoinjs-lib to v7

[landabaso]

This PR is a follow up to #428. It enables descriptors v3 support and aligns dependencies with the current bitcoinjs-lib major.

• Migrate third-party address validation to @bitcoinerlab/descriptors v3 (DescriptorsFactory + Output), enabling tapscript address validation.
• Extend appClient wallet-address integration vectors with additional testnet descriptor/address cases from Python coverage.
• Upgrade bitcoinjs-lib from 6.x to 7.x
• Upgrade the TS/JS toolchain to current versions (TypeScript 5.9, Jest 30, ts-jest, babel-jest, typedoc 0.28) and set node >= 18.14 (required by bitcoinjs-lib / @bitcoinerlab/descriptors).
• Keep the library API non-breaking by converting v7 Uint8Array/bigint values internally to existing Buffer/number interfaces.
• A future major release can switch public return types to Uint8Array/bigint if desired.

[landabaso]

BTW, I added a console.warn when descriptor parsing fails. The musig key expression is currently unsupported in @bitcoinerlab/descriptors, so those cases warn. I can remove the warning if you prefer.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.81%. Comparing base (96b0077) to head (64ff291).
⚠️ Report is 14 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #430      +/-   ##
===========================================
- Coverage    85.96%   85.81%   -0.16%     
===========================================
  Files           30       18      -12     
  Lines         3476     2812     -664     
  Branches       520      425      -95     
===========================================
- Hits          2988     2413     -575     
+ Misses         477      388      -89     
  Partials        11       11              

Flag	Coverage Δ
unittests	85.81% <ø> (-0.16%)	⬇️

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[Copilot]

Pull request overview

This PR migrates the bitcoin_client_js library from bitcoinjs-lib v6 to v7 and @bitcoinerlab/descriptors v1 to v3, enabling tapscript address validation while maintaining API backward compatibility through internal type conversions.

Changes:

• Upgraded bitcoinjs-lib from 6.x to 7.x and @bitcoinerlab/descriptors from 1.x to 3.x, with TypeScript/Jest toolchain updates
• Added type conversion helpers (asBuffer, asSatoshiNumber) to convert bitcoinjs-lib v7's Uint8Array/bigint to Buffer/number throughout psbtv2.ts
• Migrated address validation from Descriptor to Output API, enabling tapscript support and extending test coverage with taproot descriptor cases

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
bitcoin_client_js/package.json	Updated dependencies: bitcoinjs-lib ^7.0.1, @bitcoinerlab/descriptors ^3.0.6, Jest/TypeScript toolchain upgrades, node >=18.14 requirement
bitcoin_client_js/src/lib/psbtv2.ts	Added asBuffer/asSatoshiNumber conversion helpers; wrapped all bitcoinjs-lib v7 Uint8Array/bigint values in Transaction and Psbt operations
bitcoin_client_js/src/lib/policy.ts	Wrapped crypto.sha256 return values with Buffer.from to handle Uint8Array
bitcoin_client_js/src/lib/merkle.ts	Added sha256AsBuffer helper function to convert crypto.sha256 Uint8Array output to Buffer
bitcoin_client_js/src/lib/clientCommands.ts	Wrapped crypto.sha256 return value with Buffer.from for preimage handling
bitcoin_client_js/src/lib/appClient.ts	Migrated from Descriptor({expression, network}) to Output({descriptor, network}) API; updated error handling comments for v3 tapscript support
bitcoin_client_js/src/tests/appClient.test.ts	Added 6 new test cases covering sh(sortedmulti), sh(wsh(sortedmulti)), tr() taproot descriptors, and musig policies from Python test suite
bitcoin_client_js/jest.config.js	Added testPathIgnorePatterns to exclude build directory from test runs

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