refactor(starknet): replace BlockStatus string with typed enum

[0xsamalt]

• Introduces BlockStatus as a typed uint8 enum in starknet/block.go with constants BlockPending, BlockAcceptedOnL1, BlockAcceptedOnL2, BlockRejected, and BlockPreConfirmed
• Adds UnmarshalText so the feeder JSON response deserialises directly into the enum and invalid status strings now return an error
• Updates all comparison sites and test assertions to use the typed constants

[Ehsan-saradar]

Nice one, typed status is much better than a bare string 👍

One thing I'd double-check first though: UnmarshalText now errors on any status that isn't one of the five, and since blocks are decoded straight through json.Unmarshal, an unknown status fails the whole block decode — not just that field. With the old string we accepted anything and only really cared about PENDING / PRE_CONFIRMED.

So if the feeder ever sends something not in the list (pretty sure ABORTED / REVERTED can show up on blocks), we'd fail to read that block and sync would get stuck on it.

Wdyt about mapping unknown values to a BlockUnknown instead of erroring? Keeps it harmless like before, since we only check for PENDING / PRE_CONFIRMED anyway. Or if we'd rather keep it strict, probably worth confirming the list covers everything the gateway can actually send.