bun-compat: implement the bun:jsc heapStats surface #9743

Problem

Perry's parity table lists the entire bun:jsc module as unsupported. Bun-target applications can use heapStats() for optional memory diagnostics, including through a dynamic import. Perry currently warns that bun:jsc cannot be resolved.

This issue intentionally covers only the small heapStats surface, not the profiler, debugger, or JSC optimization-control APIs.

Minimal repro

const { heapStats } = await import("bun:jsc");
const stats = heapStats(true);

console.log(typeof stats.heapSize);
console.log(typeof stats.objectCount);
console.log(typeof stats.objectTypeCounts);
console.log(typeof stats.protectedObjectTypeCounts);
console.log(typeof stats.mimalloc);

Bun 1.3.14 prints five lines containing number, number, object, object, object.

The currently observable key set is:

extraMemorySize
globalObjectCount
heapCapacity
heapSize
mimalloc
objectCount
objectTypeCounts
protectedGlobalObjectCount
protectedObjectCount
protectedObjectTypeCounts

Acceptance criteria

• bun:jsc resolves as a built-in in Bun-platform compilations without an unresolved-import warning.
• Static import, await import("bun:jsc"), and require("bun:jsc") expose the same heapStats function.
• heapStats() and the compatibility spelling heapStats(true) return the keys above.
• Scalar counters are finite, non-negative numbers.
• objectTypeCounts, protectedObjectTypeCounts, and mimalloc are objects whose reported counters are finite, non-negative numbers.
• Values describe Perry's own heap/allocator where an exact JavaScriptCore concept does not exist; the implementation documents any intentionally approximate counters.
• A compiled-binary test checks shape, types, monotonic sanity, and both argument forms without asserting machine-specific counts.

Upstream Bun uses this surface for leak diagnostics and its Node v8 compatibility layer.