fix(grpc): return actual earliest_store_height in node.Status endpoint

[Cordtus]

Description

Closes: #15463

This PR implements the EarliestVersion() method on the MultiStore interface to enable querying the earliest available state height. This addresses the longstanding TODO in the Status gRPC endpoint that was returning 0 for EarliestStoreHeight.

Problem

Indexers and tooling need to know which heights a pruned node can serve queries for. Currently:

• earliest_block_height in Tendermint's STATUS RPC returns the earliest block, not the earliest state
• The EarliestStoreHeight field in cosmos.base.node.v1beta1.Status was hardcoded to 0

Solution

• Add EarliestVersion() int64 to the MultiStore interface
• Implement persistent tracking in rootmulti.Store:
  • Stores earliest version at s/earliest key
  • Defaults to 1 for unpruned chains
  • Updates after successful pruning in PruneStores()
• Add panic implementation in cachemulti.Store (consistent with LatestVersion())
• Update Status gRPC endpoint to return the actual earliest store height

Changes

File	Change
store/types/store.go	Add EarliestVersion() to MultiStore interface
store/rootmulti/store.go	Implement EarliestVersion(), GetEarliestVersion(), flushEarliestVersion()
store/cachemulti/store.go	Add panic implementation
client/grpc/node/service.go	Use EarliestVersion() instead of hardcoded 0
store/rootmulti/store_test.go	Add 3 unit tests

Testing

• TestEarliestVersion - basic functionality, default value
• TestEarliestVersionWithPruning - tracks updates after pruning
• TestEarliestVersionPersistence - persists across restarts

=== RUN   TestEarliestVersion
--- PASS: TestEarliestVersion (0.00s)
=== RUN   TestEarliestVersionWithPruning
--- PASS: TestEarliestVersionWithPruning (0.00s)
=== RUN   TestEarliestVersionPersistence
--- PASS: TestEarliestVersionPersistence (0.00s)

API Changes

This is a breaking change for any code implementing the MultiStore interface - they must now implement EarliestVersion() int64.

[fmorency]

Would love to get this backported to 0.50.x. It would enable fixing manifest-network/yaci#28

[aljo242]

This seems like a nice feature but will need more extensive testing such as using systemtest if we are going to include

[Cordtus]

Added systemtest for the node.Status gRPC endpoint:

• Basic test confirms valid heights are returned
• Pruning test configures aggressive state pruning and confirms earliest_store_height increases afterward

Also updated the service to use CommitMultiStore directly since query context provides a CacheMultiStore which doesn't support version queries.

Run locally:

make build && cp build/simd tests/systemtests/binaries/
cd tests/systemtests && go test -tags system_test -v -run TestNodeStatus

[fmorency]

@aljo242 is there anything blocking this PR?