store: Make "grpc_max_decoding_message_size" configurable & Enable gRPC gzip compression

[pingyu]

Changes

• Enable gRPC gzip support by turning on tonic’s gzip feature and configuring the store gRPC client to accept gzip-compressed responses (cherry pick store: Make "grpc_max_decoding_message_size" configurable #485).
• Add grpc_max_decoding_message_size to client Config (default 4MB) with a builder method, and wire it through PD/store connection setup so gRPC clients use the configured decode limit (cherry pick store: Enable gRPC gzip compression #490).
• Update example TiKV config to use server.grpc-compression-type = "gzip" (config/tikv.toml).
• Bump crate version to 0.4.0 (Cargo.toml) as the new config item grpc_max_decoding_message_size may break client codes.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: coocood, iosmanthus

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-20 08:12:49.891221195 +0000 UTC m=+481597.505178051: ☑️ agreed by iosmanthus.
• 2026-01-20 08:59:17.861779451 +0000 UTC m=+484385.475736297: ☑️ agreed by coocood.