* [Enhancement] Introduce LetWrapper for handling loop variable substitutions in pipeline rewriting
* Added LetWrapper struct to encapsulate variable and value pairs for loop variable substitutions.
* Updated PipelineRewriter to accept a vector of LetWrapper instances, allowing for proper handling of Let statements that depend on the pipeline loop variable.
* Enhanced the BuildPipeline method to incorporate LetWrapper instances into rewritten blocks, ensuring correct substitutions during pipeline execution.
* Refactored logic for processing Let statements to differentiate between those that use the loop variable and those that do not, improving the flexibility of the pipeline transformation.
* Refactor lambda expression for clarity in loop variable usage check in inject_pipeline.cc
* [Test] Add regression test for loop variable handling in kernel compilation
* Introduced a new test case to verify correct handling of loop variables in the kernel compilation process, addressing a regression issue with InjectSoftwarePipeline.
* The test ensures that the loop variable is not left as a free variable, which previously caused failures in MakePackedAPI.
* Configurations are set to disable warp specialization and TMA lowering to align with the original issue reproduction.
* Remove unused import in regression test for loop variable handling in kernel compilation
