Allow multiple transaction extension version in UncheckedExtrinsic type.

[gui1117]

This PR enhance UncheckedExtrinsic type with a new optional generic: ExtensionOtherVersion.
This generic defaults to InvalidVersion meaning there is not other version than the regular version 0. This is the same behavior as before this PR.

New feature

To use this new feature, you can use the new types TxExtLineAtVers and MultiVersion to define a transaction extension with multiple version:

pub type TransactionExtensionV0 = ();
pub type TransactionExtensionV4 = ();
pub type TransactionExtensionV7 = ();

pub type OtherVersions = MultiVersion<
	TxExtLineAtVers<4, TransactionExtensionV4>;
	TxExtLineAtVers<7, TransactionExtensionV7>;
>;

pub type UncheckedExtrinsic = generic::UncheckedExtrinsic<
	AccountId,
	RuntimeCall,
	UintAuthorityId,
	TransactionExtensionV0, // The version 0, same as before
	OtherVersions, // The other versions.
>;

Breaking change

The types Preamble, CheckedExtrinsic and ExtrinsicFormat also have this new optional generic. Their type definition also have changed a bit, the General variant was 2 fields, the version and the extension, it is now only one field, the extension, and the version can be retrieve by calling extension.version()

The type inference for those types may fail because of this PR, to update the code, write some partial type: UncheckedExtrinsic<_, _, _, _>, Preamble<_, _, _>, ExtrinsicFormat<_, _> and CheckedExtrinsic<_, _, _>`.

Alternative implementation

This PR breaks the types a bit, I think it is very minimal and fine, but if this is annoying we can still keep the old types and write new types such as UncheckedExtrinsicV2, CheckedExtrinsicV2 etc..

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/12669168934
Failed job name: test-linux-stable

[gui1117]

PR is ready for review.