docs(qec): update trt_decoder documentation for recent enhancements

[wsttiger]

Update TRT decoder documentation to reflect features introduced in commits eff6966, 2954c01, and 49bdde8, bringing it inline with other QEC decoder documentation.

Key additions:

1. CUDA Graph Optimization (commit 2954c01):

   • Document new use_cuda_graph parameter (default: True)
   • Note ~20% performance improvement from CUDA graph optimization
   • Explain automatic fallback for models with dynamic shapes

2. Batch Processing Support (commit eff6966):

   • Document automatic batch size detection
   • Explain zero-padding behavior for single syndrome decode()
   • Clarify decode_batch() requirements for batch-size multiples

3. Real-Time Decoding Integration (commit 49bdde8):

   • Add comprehensive trt_decoder_config documentation
   • Include Python and C++ examples for real-time configuration
   • Document YAML serialization support
   • Add configuration reference in python_realtime_decoding_api.rst

4. Documentation Structure Improvements:

   • Add performance characteristics section
   • Add batch processing notes
   • Include cross-references to real-time decoding examples
   • Maintain consistency with nv-qldpc and sliding_window decoder docs

Files changed:

• docs/sphinx/api/qec/trt_decoder_api.rst: Added parameters, real-time config section, and performance notes
• docs/sphinx/api/qec/python_realtime_decoding_api.rst: Added trt_decoder_config class documentation
• docs/sphinx/examples_rst/qec/realtime_decoding.rst: Added TRT decoder to decoder selection section