Make it easier to modify and recompile IR

[tzunghanjuang]

Context:

This PR introduces two new methods in frontend/catalyst/debug/compiler_functions.py.

• get_pipeline_output(fn: QJIT, pass_name: str) -> str fetches the IR string after the given pipeline pass pass_name.
• replace_ir(fn: QJIT, pass_name: str, new_ir: str) -> None overwrites the IR and specify a starting pass (exclusive) pass_name for the next compilation.

The possible options for pass_name are

• MILR: mlir, HLOLoweringPass, QuantumCompilationPass, BufferizationPass, and MLIRToLLVMDialect
• LLVM: llvm_ir, CoroOpt, O2Opt, Enzyme, and last

Note that last denotes the IR right before object file generation.

Changes:

• QJIT now has an extra flag overwrite_ir to specify the new IR for compilation.
• CompilerOptions now has an extra flag startAfterPass to specify the compilation start after the given pass.
• CompilerOutput now has an extra flag reachTargetPass to indicate if the given pass is reached.
• Update documentation Debugging Tips.

Limitations

• To get IRs from get_pipeline_output, the function must be compiled with keep_intermediate=True
• We must define a function first for recompilation.

Related GitHub Issues: [sc-67088]