feat: rest_blockfrost parameters endpoints

[whankinsiv]

This PR:

• Aligns ProtocolParamsRest fields with Blockfrost /epochs/*/parameters response format (except the nonce field which will be implemented in a later PR in epoch_activity_counter).
• Implements handle_epoch_params_blockfrost for /epochs/latest/parameters and /epochs/{number}/parameters.
• Registers placeholder REST handlers for all Blockfrost /epochs/* endpoints.
• Adds cost_models.rs defining static arrays for Plutus V1/V2/V3 cost model parameter names.
• Removes the unused active_epoch field from State.

[sandtreader]

Well done for mapping all these! It occurs to me at some point we will need to implement the fee calculation using them (shudder!) so we might need to pull this back into the common types and have them explicitly named in the parameters structures. But that's for the future...

[sandtreader]

Good work! Just one redundant info!() and conflict fix and it's good to go.