Apply PitchScript runtime and compatibility fixes - #1

Process completed with exit code 1.

AssertionError: expected 1st "spy" call to have been called with [ '```5```' ] - Expected + Received [ "```5```", + undefined, ] ❯ tests/fcdex-runtime.test.ts:121:26

AssertionError: expected "spy" to be called with arguments: [ '```5```' ] Received: 1st spy call: [ "```5```", + undefined, ] Number of calls: 1 ❯ tests/fcdex-runtime.test.ts:84:26

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/