fix(rpc): align Beacon API routes with spec and register missing handlers (#1579)

[alok-108]

What was wrong?

Several non-spec route paths and missing handler registrations in crates/rpc/beacon/ prevented standard Ethereum Beacon API compliance, resulting in 404 Not Found errors when clients (validator clients, builder relays, slashers) made standard requests:

1. Non-spec Blinded Blocks Route: GET /eth/v1/beacon/blind_block/{block_id} was exposed instead of the spec-mandated GET /eth/v1/beacon/blinded_blocks/{block_id} (Ethereum Beacon API - getBlindedBlock).
2. Proposer Slashings Pool Route & Method Typo: The endpoint was mapped with a typo as #[get("/beacon/pool/prposer_slashings")] (missing o), causing GET /eth/v1/beacon/pool/proposer_slashings to 404. Furthermore, OperationPool::get_all_proposer_slahsings contained a typo.
3. Unregistered Sync Committee Selections Handler: POST /eth/v1/validator/sync_committee_selections handler was implemented in handlers/validator.rs but never registered in register_validator_routes_v1. In addition, the spec defines the request body as an array Vec<SyncCommitteeSelection>, whereas the handler accepted a single object SyncCommitteeSelection.

Closes #1579

How was it fixed?

1. Blinded Blocks Route:
   • Changed route macro from #[get("/beacon/blind_block/{block_id}")] to #[get("/beacon/blinded_blocks/{block_id}")].
   • Renamed handler to get_blinded_block and updated its registration in routes/beacon.rs.
2. Proposer Slashings Route & OperationPool:
   • Fixed route macro to #[get("/beacon/pool/proposer_slashings")] and updated doc comment to v1.
   • Renamed OperationPool::get_all_proposer_slahsings to get_all_proposer_slashings while retaining a #[deprecated] alias for backwards compatibility.
   • Updated calls in crates/rpc/beacon/src/handlers/pool.rs and crates/rpc/beacon/src/handlers/validator.rs.
3. Sync Committee Selections:
   • Registered post_sync_committee_selections on register_validator_routes_v1.
   • Updated parameter to Json<Vec<SyncCommitteeSelection>> to adhere to the spec schema.
4. Testing & Validation:
   • Added unit test in ream-operation-pool testing get_all_proposer_slashings.
   • Added integration tests in crates/rpc/beacon/src/tests.rs verifying that:
     • GET /eth/v1/beacon/pool/proposer_slashings returns 200 OK (and old /prposer_slashings returns 404).
     • POST /eth/v1/validator/sync_committee_selections returns 501 Not Implemented with vector payload (verifying registration instead of 404).
     • GET /eth/v1/beacon/blinded_blocks/{block_id} is routed properly.
   • Verified clean formatting via cargo +nightly fmt --check.
   • Verified zero clippy warnings via cargo clippy --features devnet5 -p ream-rpc-beacon -p ream-operation-pool.

To-Do

• I have read CONTRIBUTING.md.
• This PR title follows conventional commits.

[alok-108]

Hey @KolbyML @Kayden-ML @shariqnaiyer, opened a fix for #1579 (route typos and the missing sync committee handler). Whenever you get a chance, could you approve the CI run? Thanks.