ABI: implement Bun process warning emission

Parent: #239 Depends on: #240

Implement Bun__Process__emitWarning and Bun__promises__emitUnhandledRejectionWarning over the realm-owned process EventEmitter.

Acceptance:

• Match string/Error warning normalization, name/type/code/detail/stack descriptors, and ordered warning listener delivery.
• Reproduce the two-warning unhandled-rejection path, exact own-stack classification, throwing stack reads, pure fallback stringification, and exception clearing between emissions.
• Preserve selected-realm prototypes, reason/promise identity, sibling boundaries, and listener-throw behavior.
• Add focused and pinned consumer evidence; refresh inventories/docs.

Implemented and pushed to main in d7b07fcc; generated evidence/docs followed in fe4fd380. Bun__Process__emitWarning and Bun__promises__emitUnhandledRejectionWarning now match the pinned normalization, descriptor, selected-realm, ordered delivery, own-stack/fallback, exception-clearing, and listener-failure semantics. Verification: focused 3/3 with 0 leaks; Home audit 233/431 implemented; Bun audit 227/421 implemented; consumer 232/232 linked and runtime matrix passed.