execution/engineapi: reject engine_getBlobsV1 post-osaka

[Sahil-4555]

As per the Engine API specifications, once the Osaka fork is activated on the network, we must not support the engine_getBlobsV1 method anymore and it should return the -38005: Unsupported fork error. To handle this, I have added a check in GetBlobsV1 of EngineServer to check if the current canonical head block's timestamp has crossed the Osaka activation time or not. If it is active, we are directly returning the UnsupportedForkError.

Additionally, I have also added validations for the V2 and V3 methods. Previously, if someone called engine_getBlobsV2 or engine_getBlobsV3 before Osaka activation, Erigon was querying the txpool and then returning null because the proofs were not 128 elements. But this was wasting CPU cycles by unnecessarily searching the pool and it was also spamming the logs with warning messages like "pre-Fusaka proofs, len(proof)=1" every time.

Now, with this change, if Osaka is not active, both GetBlobsV2 and GetBlobsV3 will directly return null without calling the pool.