Avoid double `structuredClone` in `generate-schema-types` compile path

[l2ysho]

Every schema compilation in actor generate-schema-types performs two full deep clones:

1. clearAllRequired(schema) / makePropertiesRequired(schema) — each does structuredClone internally
2. stripTitles(schemaToCompile) — does another structuredClone at the top of the function

All three functions guarantee immutability (tested), so the second clone in stripTitles is redundant when the caller already holds a disposable copy from step 1.

For the current schemas this has zero practical impact, but it is wasteful and worth cleaning up.

Options

Plan A — { mutate: true } flag on stripTitles

Minimal API change. When the caller already has a disposable clone, it opts out of the internal clone:

export function stripTitles(schema, { mutate = false } = {}) {
    const result = mutate ? schema : structuredClone(schema);
    // all internal recursive calls pass { mutate: true }
    ...
}

// call site — schemaToCompile is already a clone, skip second structuredClone
stripTitles(schemaToCompile, { mutate: true })

Plan B — combined prepareForCompilation(schema, allOptional) helper

Single clone, applies both the required-field transformation and title-stripping in one pass. Requires extracting private mutating helpers for each transform. Call sites become a single function call but the internal refactor is larger.

Reference

Introduced in #1000.