This commit addresses issue #9877 by implementing Promise.become() method that allows a Promise to be linked directly to a Fiber’s completion result, eliminating unnecessary allocations and callback indirection.

Key changes:

• Added Promise.become(fiber) method that links promise to fiber completion
• Optimized Promise.await() to handle LinkedToFiber state efficiently
• Enhanced Promise internal state with LinkedToFiber case
• Added comprehensive tests for the new functionality
• Created benchmark examples demonstrating performance benefits

Performance improvement: When a fiber forks work and then waits on a Promise, the traditional approach creates async suspension + callback indirection. The new approach allows direct fiber-to-fiber linkage, reducing allocations and improving performance.

/claim #9877