Elastic scaling: introduce new candidate receipt primitive (#5322)

closes https://github.com/paritytech/polkadot-sdk/issues/5044

This PR switches the runtime to the new receipts format (vstaging
primitives). I've implemented `From` to convert from new primitives to
`v7` primitives and used them in the node runtime api client
implementation. Until we implement the support in the node, it will
continue e to use the v7 primitives but the runtime apis already use the
new primitives.


An expected downside of RFC103 is decoding V2 receipts shows garbage
values if the input is V1:

_![ima_9ce77de](https://github.com/user-attachments/assets/71d80e78-e238-4518-8cd1-548ae0d74b70)_

TODO:
- [x] fix tests
- [x] A few more tests for the new primitives
- [x] PRDoc

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Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>