support left shift or right shift operator

[Lynette7]

Resolves #181

To implement right-shift and left-shift operators, here are the changes I've made:

• Added token recognition for << and >> in the lexer
• Extended Op2 enum to include RightShift and LeftShift
• Updated the parser to recognize and handle bit shift tokens
• Modified type checker to support the shift operations
• Implemented circuit writer logic for bit shifts using field arithmetic
• Implemented bit shift operations for field elements, supporting constant value shifts and cell variable shifts with constant shift amounts
• Added bitwise shift operations using logical shift right (Lshr) and shift left (Shl) in circuit IR generation

[katat]

Thanks for addressing this.

I realized this feature can be complicated to support in the constraint level, because the unit in that level is finite field. It makes sense to support logical shifting in finite field, but that can be confusing from user perspective since they might assume they are arithmetic shifting.

Therefore, I think for now we can just make it support in the hint function. That is the feature can be implemented in the ir.rs, which is based on Circ term.

Also please add tests in the examples.