* Fixed accepting integer IDs in requests for Tendermint RPC server (#2366)
* added a wrapper interface `jsonrpcid` that represents both string and int IDs in JSON-RPC requests/responses + custom JSON unmarshallers
* changed client-side code in RPC that uses it
* added extra tests for integer IDs
* updated CHANGELOG_PENDING, as suggested by PR instructions
* addressed PR comments
* added table driven tests for request type marshalling/unmarshalling
* expanded handler test to check IDs
* changed pending changelog note
* changed json rpc request/response unmarshalling to use empty interfaces and type switches on ID
* some cleanup
At larger tx sizes (e.g. > 10000) we were spending non-neglible
amounts of time in tx creation, due to making the final bytes random.
The slower the send loop, the less accurate it is at measuring the time
tendermint took. (As we can't reach the promised contract of the given rate)
There really isn't much need for that randomness, so this PR makes it
such that only the txNumber gets bumped between txs from the same
connection, thereby improving sendloop speed and accuracy.
