Upgrade project to TypeScript 6.0.3 and resolve TS6 type-system breakage

[Copilot]

This updates the repo to the latest stable TypeScript and makes the minimal compatibility changes needed so the project remains buildable and CI-ready under TS6. The upgrade surfaced a recursive type-instantiation failure in schema union handling, which this PR addresses.

• Dependency and CI alignment

  • Pinned typescript in devDependencies to 6.0.3.
  • Updated GitHub Actions matrix to install/test against 6.0.3 instead of the prior 4.x range.

• TS6 compiler compatibility

  • Added ignoreDeprecations: "6.0" to tsconfig.json to keep the existing target: "es5" configuration valid under TS6 deprecation enforcement.

• Type-level recursion fix in schema unions/intersections

  • Reworked AnyOfType / OneOfType / AllOfType evaluation from mapped-index expansion to direct union extraction to avoid TS6 “excessively deep and possibly infinite” instantiation.

// before
T extends AnyOfType<infer U> ? { [K in keyof U]: TSType<U[K]> }[number]

// after
T extends AnyOfType<infer U> ? TSType<U[number]>

Original prompt

Upgrade the repository dependency on TypeScript to the latest available version and make any necessary code, config, or test updates so the project builds and tests pass.

Repository: ptpt/json-schema-ts

Requirements:

• Update TypeScript-related dependency declarations to the latest stable TypeScript version.
• Adjust any tsconfig, build scripts, lint config, or test config required for compatibility.
• Fix any type errors, compilation issues, or test failures introduced by the upgrade.
• Ensure the repository remains functional and CI-ready after the upgrade.
• Create a pull request with the changes.

Please inspect the repository to determine the current package manager, dependency locations, test/build commands, and any compatibility constraints before making changes.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: upgrade @ptpt/json-schema-ts to latest typescript

Assistant: What repository should I make that change in? If you mean the package repo itself, please confirm ptpt/json-schema-ts. Also, do you want me to just tell you the latest TypeScript version and the likely changes needed, or actually open a PR?What repository should I make that change in? If you mean the package repo itself, please confirm ptpt/json-schema-ts. Also, do you want me to just tell you the latest TypeScript version and the likely changes needed, or actually open a PR?

User: open a PR

Assistant: I’ve started the PR creation flow for ptpt/json-schema-ts and I’m waiting for the repository task to finish.

This pull request was created from Copilot chat.