feat(field): add PowPFOp to support prime field exponent

[quanxi1]

Description

This PR introduces PowPFOp which can take prime field element as an exponent so that HLO power operation can handle both scalar field type and primitive unsigned integer type as an exponent.

Related Issues/PRs

• fix: remove sign check from PowOp #61

Checklist

• Branch name follows Branch Guideline
• Commit messages follow Commit Message Guideline
• Checked Pull Request Guideline

[quanxi1]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces PowPFOp to support exponentiation where the exponent is a prime field element. This is a great feature that enhances the flexibility of power operations. The implementation refactors the existing PowUIOp logic into a shared computePower helper function, which is a clean approach to avoid code duplication. The new functionality is also well-tested. I have one suggestion to improve the readability of the computePower function for better long-term maintainability.

[gemini-code-assist]

The modulus variable is reused to store the group order (p^2 - 1), which can be confusing as it originally holds the prime modulus p. Using a separate, more descriptively named variable like groupOrder would make the logic for exponent reduction clearer and improve maintainability.

Suggested change

	modulus = modulus.zext(modBitWidth * 2);
	modulus = modulus * modulus - 1;
	exp = b.create<arith::ExtUIOp>(
	IntegerType::get(exp.getContext(), modulus.getBitWidth()), exp);
	intType = IntegerType::get(exp.getContext(), modulus.getBitWidth());
	exp = b.create<arith::RemUIOp>(
	exp, b.create<arith::ConstantIntOp>(intType, modulus));
	APInt groupOrder = modulus.zext(modBitWidth * 2);
	groupOrder = groupOrder * groupOrder - 1;
	exp = b.create<arith::ExtUIOp>(
	IntegerType::get(exp.getContext(), groupOrder.getBitWidth()), exp);
	intType = IntegerType::get(exp.getContext(), groupOrder.getBitWidth());
	exp = b.create<arith::RemUIOp>(
	exp, b.create<arith::ConstantIntOp>(intType, groupOrder));

[chokobole]

chore(feat): fix description: the scope should be field