e13b4386ff
`abci.Client`:
- Sync and Async methods now accept a context for cancellation
* grpc client uses context to cancel both Sync and Async requests
* local client ignores context parameter
* socket client uses context to cancel Sync requests and to drop Async requests before sending them if context was cancelled prior to that
- Async methods return an error
* socket client returns an error immediately if queue is full for Async requests
* local client always returns nil error
* grpc client returns an error if context was cancelled before we got response or the receiving queue had a space for response (do not confuse with the sending queue from the socket client)
- specify clients semantics in [doc.go](https://raw.githubusercontent.com/tendermint/tendermint/27112fffa62276bc016d56741f686f0f77931748/abci/client/doc.go)
`mempool.TxInfo`
- add optional `Context` to `TxInfo`, which can be used to cancel `CheckTx` request
Closes #5190
Tendermint RPC
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