feat: add symbolic stack backend path

[tcrypt25519]

Summary

• add a selectable symbolic stack backend and monomorphized stack operations
• advance symbolic control-flow handling, including dynamic JUMP/JUMPI through conservative site-local switches
• document the symbolic-stack roadmap and current CFG limitations

Verification

• cargo check -p jet
• cargo test -p jet --test test_roms
• JET_SYMBOLIC_STACK=1 cargo test -p jet --test test_roms
• cargo clippy -p jet --all-targets -- -D warnings

[semanticdiff-com]

Review changes with  

[gemini-code-assist]

Code Review

This pull request introduces a symbolic stack lowering path to the Jet EVM JIT compiler, enabling compile-time tracking of stack values and more efficient IR generation. It refactors opcode implementations to use a generic StackBackend trait, supporting both runtime and symbolic modes, and upgrades the project to LLVM 22. A new jetdbg CLI tool is also included for contract debugging. Review feedback identifies a bug in the symbolic handling of PUSH data where bytes are incorrectly reversed, and recommends using safe Inkwell methods to replace unnecessary unsafe blocks in the stack backend implementation.

[gemini-code-assist]

The reverse() call here appears to be a bug. According to the architecture documentation and the instructions::Iter implementation, PUSH data is already converted to little-endian (bytes reversed) by the iterator. Since ops::push expects little-endian bytes to construct its i256 limbs, reversing them again here will turn them back into big-endian, leading to incorrect values for multi-byte PUSH opcodes.

                ops::push(bctx, new_data)?;

[gemini-code-assist]

The use of unsafe and as_value_ref() here is unnecessary. Since loaded is a BasicValueEnum resulting from an i256 load, you can use the safe into_int_value() method provided by Inkwell.

Suggested change

	let word = unsafe { IntValue::new(loaded.as_value_ref()) };
	let word = loaded.into_int_value();

[gemini-code-assist]

The use of unsafe and as_value_ref() can be avoided here by using into_pointer_value() on the result of the peek call.

Suggested change

	let ptr = unsafe { PointerValue::new(ret.as_value_ref()) };
	let ptr = ret.try_as_basic_value().left().unwrap().into_pointer_value();