Fix deep recursion in ResourceBasedSlotSupplier causing futures to never resolve

[tconley1428]

Summary

• Fixed a critical bug where ResourceBasedSlotSupplier futures would never complete due to deep recursion in CompletableFuture chains
• Replaced recursive thenCompose() chaining with iterative polling using ScheduledExecutorService
• Added comprehensive test suite to verify the fix and prevent regressions

Problem

The previous implementation in scheduleSlotAcquisition() used recursive CompletableFuture chaining that could create very deep call stacks. When resource starvation lasted for extended periods, this would result in chains of thousands of nested futures that would never resolve even after resources became available, due to stack depth issues and recursive completion problems.

Solution

Replaced the recursive approach with:

1. Iterative polling mechanism using ScheduledExecutorService.schedule()
2. Proper cancellation handling with AtomicReference<ScheduledFuture<?>>
3. Maintained timing contracts - still respects ramp throttle delays
4. Added minimum 10ms delay to prevent tight spinning
5. Preserved all existing API behavior and contracts

Test Results

All tests in ResourceBasedSlotSupplierNonRecursiveTest now pass:

• ✅ testFutureNeverResolvesEvenAfterResourcesBecomeAvailable - FIXED: Future now completes in ~1-9ms instead of never completing
• ✅ testFutureCancellationWithRecursiveChain - Proper cancellation still works
• ✅ testMemoryAndPerformanceImpactOfDeepRecursion - Performance maintained
• ✅ All other existing behavior preserved

Test plan

• Run ResourceBasedSlotSupplierNonRecursiveTest - all tests pass
• Verify the main bug fix: futures complete immediately when resources become available
• Verify no regressions in cancellation, memory usage, or timing behavior
• Code compiles and builds successfully

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