make STObjectType generic

[surangap]

    not 100% sure if these will work but rough ideas (I prefer 2 because of the nicer syntax)

Idea 1

use tuple as the field inner type, see: https://crates.io/crates/impl-trait-for-tuples

#[derive(Field, Debug, Clone)]
pub struct SignerEntry(pub (Account, SignerWeight))

use impl_for_tuples::impl_for_tuples;

// support field objects with upto 5 items
#[impl_for_tuples(5)]
impl BinarySerialize for TupleIdentifier {
    fn binary_serialize_to(buf, for_signing) {
        for_tuples!( #( TupleIdentifier.binary_serialize_to(buf, for_signing) )* );
    }
}

#[impl_for_tuples(5)]
impl CodecField for TupleIdentifier {
    fn field_code(&self) -> u16 {
        for_tuples!( #( TupleIdentifier.field_code() )* );
    }
    fn type_code(&self) -> u16 {
        for_tuples!( #( TupleIdentifier.type_code() )* );
    }
    fn is_variable_length(&self) -> bool {
        for_tuples!( #( TupleIdentifier.is_variable_length() )* );
    }
    fn is_serialized(&self) -> bool {
        for_tuples!( #( TupleIdentifier.is_serialized() )* );
    }
    fn is_signing_field(&self) -> bool {
        for_tuples!( #( TupleIdentifier.is_signing_field() )* );
    }
    fn inner(&self) -> &dyn BinarySerialize {
        for_tuples!( #( TupleIdentifier.inner() )* );
    }
}

Idea 2

Transaction is basically STObject only missing the Field trait

// this will behave as an 'STObject'
#[derive(Field, STObject, Debug, Clone)]
pub struct SignerEntry {
    account: Account,
    weight: SignerWeight
}

• implement CodecToFields for Field (macro might needs some changes to parse the above syntax)
• Could then rename 'Transaction' trait/macro to 'STObject'

change the serialize for Field to do this instead:

xrpl-tx-codec/codec/src/field.rs

Line 93 in 6765c85

let mut data = self.inner().binary_serialize(for_signing);

for f in &self.to_canonical_fields() {
    f.binary_serialize_to(buf, for_signing)
}

Originally posted by @jordy25519 in #5 (comment)