Add create_mcjit_execution_engine_with_memory_manager for custom MCJIT memory management

[ktanaka101]

---

Description

This PR adds a new function, create_mcjit_execution_engine_with_memory_manager, which allows users to supply their own JIT memory manager (McjitMemoryManager trait). This enables custom allocation, finalization, and teardown logic for code and data sections under MCJIT.

Related Issue

Close #296

How This Has Been Tested

Tested on a Mac M1 MAX host running Docker (Debian bookworm),
with LLVM 18 installed inside the container.

• Manually and testcode verified on AArch64 Linux with a small JIT-compiled function.

  f64 test_fn() {
  entry:
    call void @llvm.experimental.stackmap(i64 12345, i32 0)
    ret f64 64.0
  }
  

• Confirmed that user-defined allocate_code_section, allocate_data_section, finalize_memory, and destroy callbacks are invoked by MCJIT.
• No regressions observed in existing tests (the standard test suite still passes).

Checklist

• I have read the Contributing Guide
• My code follows the style and guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works

---

Changes

1. New Public API

   pub fn create_mcjit_execution_engine_with_memory_manager(
       &self,
       memory_manager: impl McjitMemoryManager + 'static,
       opt_level: OptimizationLevel,
       code_model: CodeModel,
       no_frame_pointer_elim: bool,
       enable_fast_isel: bool,
   ) -> Result<ExecutionEngine<'ctx>, LLVMString> {
       // ...
       // Implementation that boxes the memory manager, creates an LLVMMCJITMemoryManager, 
       // and finalizes the MCJIT options before returning an `ExecutionEngine`.
       // ...
   }

2. McjitMemoryManager Trait

   • Allows the user to override how code/data sections are allocated and finalized.
   • Includes allocate_code_section, allocate_data_section, finalize_memory, and destroy.

3. MemoryManagerAdapter

   • Internal struct used to connect user-defined trait implementations to LLVM’s C callbacks (allocate_code_section_adapter, allocate_data_section_adapter, etc.).
   • Automatically cleans up the memory manager upon destroy().

By merging this PR, Inkwell will support custom JIT memory management for MCJIT, addressing use cases like:

• Allocating executable code in custom memory pools.
• Intercepting .llvm_stackmaps for garbage collection.
• Applying security restrictions or sandboxing JIT-compiled code.

Thank you for reviewing!

[ktanaka101]

Thank you for the review. I've addressed all of your comments.

[TheDan64]

Thanks!