Function validate_p2pkh 

pub fn validate_p2pkh(
    script_sig: &[u8],
    script_pubkey: &[u8],
) -> Result<bool, ScriptError>

Validates a Pay-to-Public-Key-Hash (P2PKH) script pair.

Executes script_sig (the unlocking script) on a fresh stack, then executes script_pubkey (the locking script) on the resulting stack. This two-phase model matches Bitcoin’s actual execution behavior (post-2010), preventing scriptSig from manipulating scriptPubKey’s control flow.

Returns Ok(true) if the combined execution succeeds (top stack element is truthy after both phases).

OP_CHECKSIG uses stub mode (always succeeds). For real ECDSA verification, use validate_p2pkh_with_opts with a sighash and the secp256k1 feature enabled.

Both arguments are raw script bytes (not hex). Use crate::hex::decode_hex to convert hex strings first.