chore: upgrade gRPC to 1.84.0

[merlimat]

Stacked on #417 (Netty 4.2.18). Until that merges, this diff also shows its commit. Only chore: upgrade gRPC to 1.84.0 is new here.

Motivation

The client is on gRPC 1.75.0. 1.84.0 is the latest release, and since 1.83.0 grpc-java has been built and tested against Netty 4.2, which the client moves to in #417.

Modifications

• Bump grpc from 1.75.0 to 1.84.0 in gradle/libs.versions.toml.
• Bump proto-google-common-protos from 2.59.2 to 2.64.1, the version grpc-protobuf 1.84.0 declares. The client lists it as a direct runtime dependency in its published POM. If it stayed at 2.59.2, Maven's nearest-wins rule would give Maven users 2.59.2 under grpc-protobuf 1.84. Gradle builds already resolved 2.64.1.

Release notes for 1.76 through 1.84, checked against the client:

• RFC 3986 target parsing is on by default (1.83). Connection passes the server address to Grpc.newChannelBuilder without a scheme (host:port, after removing tls://). In 1.84 the RFC 3986 path keeps the old fallback: a target that doesn't look like scheme:/... is resolved as dns:///<target>. So localhost:6648, 127.0.0.1:6648 and [::1]:6648 resolve as before.
• Netty 4.2 required (1.83). Netty is 4.2.18.Final from chore: upgrade Netty to 4.2.18.Final #417. grpc-netty 1.84 asks for 4.2.16, and the Netty BOM aligns it to 4.2.18.
• Other API and behavior changes are in xDS, binder, okhttp, Android, custom LoadBalancers and SPIFFE, none of which the client uses. The one internal class it imports, io.grpc.internal.BackoffPolicy, is unchanged.
• Transitive updates: guava 33.5.0 → 33.6.0, gson 2.11.0 → 2.14.0, protobuf-java-util 3.25.8 → 3.25.9, animal-sniffer-annotations 1.24 → 1.27. protobuf-java stays at 4.34.0, set by the existing constraint.

Verification

• ./gradlew :client:dependencies --configuration runtimeClasspath resolves all 10 io.grpc modules to 1.84.0 and all 15 io.netty modules to 4.2.18.Final. The generated POM lists proto-google-common-protos 2.64.1.
• ./gradlew build passes locally: 393 tests, no failures or skips, and no new compiler warnings. That includes all 7 Docker IT classes against a real Oxia server: OxiaClientIT, ClientReconnectIT, OxiaClientFailFastIT, RpcProviderIT, ShardSplitSessionIT, SharedResourcesIT and NotificationIt.