[RL-Kernel] Productionize linear_logp telemetry

[inaniloquentee]

Closes #20.

Depends on #17, #18, and #19. #16 is already merged; this branch was built from the refreshed rlk-main and then stacked on the Phase 1 heads.

Summary

• route Megatron actor selected-logprob replay through the Phase 1 RL-Kernel operator adapter without direct production rl_engine imports
• add linear_logp support matrix, fallback/runtime metadata, operator timing counters, and optional CUDA memory-probe metrics
• preserve native materialized-logits fallback for disabled/unsupported cases including entropy, CP, top-p replay, missing ops, and TP interface mismatch
• document the linear_logp controls, support matrix, and telemetry surface

Validation

• py -3.13 -m compileall vime\\backends\\megatron_utils\\rl_kernel.py vime\\backends\\megatron_utils\\loss.py vime\\backends\\megatron_utils\\model.py vime\\utils\\rl_kernel.py tests\\test_rl_kernel_linear_logp_integration.py tests\\_unit_stubs.py
• py -3.13 -m pytest tests\\test_rl_kernel_operator_adapter.py tests\\utils\\test_rl_kernel_execution.py tests\\test_rl_kernel_linear_logp_integration.py tests\\test_megatron_argument_validation.py tests\\test_cp_utils.py tests\\test_loss_cp_invariance.py -q
• py -3.13 -m ruff check vime\\backends\\megatron_utils\\rl_kernel.py vime\\backends\\megatron_utils\\loss.py vime\\backends\\megatron_utils\\model.py vime\\utils\\rl_kernel.py tests\\test_rl_kernel_linear_logp_integration.py tests\\_unit_stubs.py

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