Add per-context interrupt budget

[dannote]

Add a context-local interrupt counter and optional limit.

The counter increments when the interpreter reaches the existing interrupt polling path. If a context limit is set and the counter reaches it, that context throws interrupted before consulting the runtime-level interrupt handler. A limit of 0 keeps the feature disabled.

This is useful for embedders that host multiple JSContext instances inside one JSRuntime and need each context to have an independent execution budget. In QuickBEAM, a pool worker owns one JSRuntime and creates many contexts with JS_NewContext(rt). A runtime-level interrupt handler remains useful as a global guard, but it cannot express a per-context budget for that pooled model.

Tested:

cmake --build build --target api-test -j2
./build/api-test