[FEAT] Implement hEEA method to accelerate signature verification

[zz-sol]

Joint work with @samkim-crypto.

This PR implements the HEEA verification method in "Accelerating EdDSA Signature Verification with Faster Scalar Size Halving" (TCHES 2025).

It implements a new verification API verify_heea which mimiks the exact behaviour of Zebra's verify but using hEEA to accelerate the multiplications.

Cross ref: dalek-cryptography/curve25519-dalek#856

• this PR relies on [FEAT] Implement hEEA method to accelerate signature verification dalek-cryptography/curve25519-dalek#856 for backend arithmetics
• this PR implements the Zebra verification; where as [FEAT] Implement hEEA method to accelerate signature verification dalek-cryptography/curve25519-dalek#856 uses strict verification

Benched on a MBP M4ProMax

Single Verification/ed25519_zebra
                        time:   [17.196 µs 17.246 µs 17.298 µs]
                        
Single Verification/ed25519_hEEA
                        time:   [14.449 µs 14.490 µs 14.534 µs]

[natalieesk]

Thanks for this, we'll take a look

[zz-sol]

Hi gently ping to see if there is any updates on this PR? (Know you guys are going through some changes. if there is a different code base I should send this PR to, please LMK)

[conradoplg]

I see you're getting great feedback in dalek-cryptography/curve25519-dalek#856 which will probably apply here, so I'm inclined to wait until it merges there. I will try to help review it there too.