Bun parity: align BroadcastChannel custom inspect state

Scope

Continue the contiguous Bun corpus from #66 at position 4089:

• js/web/broadcastchannel/broadcast-channel.test.ts

Current gap

The first ten BroadcastChannel behavior tests reach the final custom-inspect assertion, where Home exposes bootstrap implementation fields instead of Bun's public diagnostic shape.

Expected:

BroadcastChannel { name:
   'hello',
  active:
   true }

Current Home output includes internal fields such as onmessage, onmessageerror, __home_bc_closed, and __home_bc_listeners.

The failing test also verifies that user util.inspect options (compact: true, breakLength: 2) are forwarded through the custom inspector.

Acceptance criteria

• expose Bun's BroadcastChannel { name, active } custom-inspect shape
• hide adapter implementation fields from inspection
• forward user inspect options without hard-coded formatting
• preserve behavior/lifecycle tests in the same upstream file
• pass all 11 upstream tests with no TODO or unsupported accounting
• add a focused permanent inspect regression with useful operation/cause stack diagnostics if formatting fails

Follows the worker teardown fix in #326.

Completed in c1415027a (fix(runtime): align BroadcastChannel inspection) and pushed to main.

Implemented Bun's custom inspection contract for BroadcastChannel:

• renders only { name, active }
• forwards caller inspection options and decrements nested depth like Bun
• reflects live closed state
• keeps Home's registry/listener bookkeeping non-enumerable
• adds a permanent regression for exact multiline formatting, closed-state output, and hidden adapter internals

Verification:

• upstream js/web/broadcastchannel/broadcast-channel.test.ts: 11 passed, 0 failed, 0 unsupported
• permanent focused BroadcastChannel regression: passed
• contiguous follow-ups at positions 4090-4091: 2 files, 2 passed, 0 failed, 0 unsupported
• zig fmt --check packages/home_test/src/corpus_runner.zig: passed
• zig build: passed