collation-generation: Avoid using `para_backing_state` if runtime is ancient (#4070)
fixes https://github.com/paritytech/polkadot-sdk/issues/4067
Also add an early bail out for look ahead collator such that we don't
waste time if a CollatorFn is not set.
TODO:
- [x] add test.
- [x] Polkadot System Parachain burn-in.
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Signed-off-by: Andrei Sandu <[email protected]>