fix: memory leak - grpc plugin was accumulating updates endlessly (#305)

this was caused by the bug introduced during solana upgrade, when
commitment level for updates was changed to Finalized, but filter in
plugin wasn't updated to match that

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## Greptile Summary

This PR fixes a critical memory leak in the gRPC plugin by correcting
the commitment level check for slot messages.

- Updates commitment level check from `Processed` to `Finalized` in
`magicblock-geyser-plugin/src/grpc.rs` to match current slot behavior
- Fixes memory leak caused by accumulating unprocessed slot data due to
incorrect commitment level filtering
- Improves memory management by enabling proper cleanup of old slot data
- Changes empty match arm from `_ => {}` to `_ => ()` for code
consistency



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Co-authored-by: Gabriele Picco <piccogabriele@gmail.com>

Author: bmuddha

magicblock-geyser-plugin/src/grpc.rs

@@ -168,9 +168,9 @@ impl GrpcService {
                         Message::Slot(msg) if processed_first_slot.is_none() && msg.status == CommitmentLevel::Processed => {
                             processed_first_slot = Some(msg.slot);
                         }
-                        // NOTE: this used to guard to `CommitmentLevel::Finalized`, but we never
-                        // send that
-                        Message::Slot(msg) if msg.status == CommitmentLevel::Processed => {
+                        // Note: all slots received by plugin are Finalized, as
+                        // we don't have forks or the notion of slot trees
+                        Message::Slot(msg) if msg.status == CommitmentLevel::Finalized => {
                             // NOTE: originally 10 slots were kept here, but we about 80x as many
                             // slots/sec
                             if let Some(msg_slot) = msg.slot.checked_sub(80) {
@@ -220,7 +220,7 @@ impl GrpcService {
                                 }
                             }
                         }
-                        _ => {}
+                        _ => ()
                     }
 
                     // Update block reconstruction info