* SDK: Split new `FeeRateGovernor` out of `FeeCalculator`
Leaving `FeeCalculator` to *only* calculate transaction fees
* Replace `FeeCalculator` with `FeeRateGovernor` as appropriate
* Expose recent `FeeRateGovernor` to clients
* Move `burn()` back into `FeeCalculator`
Appease BPF tests
* Revert "Move `burn()` back into `FeeCalculator`"
This reverts commit f3035624307196722b62ff8b74c12cfcc13b1941.
* Adjust BPF `Fee` sysvar test to reflect removal of `burn()` from `FeeCalculator`
* Make `FeeRateGovernor`'s `lamports_per_signature` private
* rebase artifacts
* fmt
* Drop 'Recent'
* Drop _with_commitment variant
* Use a more portable integer for `target_signatures_per_slot`
* Add docs for `getReeRateCalculator` JSON RPC method
* Don't return `lamports_per_signature` in `getFeeRateGovernor` JSONRPC reply
* SDK: Refactor (read|write)_keypair
Split file opening and data writing operations
Drop filename == "-" stdio signal. It is an app-level feature
* keygen: Move all non-key printing to stderr
* keygen: Adapt to SDK refactor
* keygen: Factor keypair output out to a helper function
* implement per-thread, per-batch sleep in ms (throttling allows easier UI development)
* tidy up sleep() call with Duration::from_millis() instead of Duration::new()
* fixup indentation style
* removing multinode-demo/client-throttled.sh (same functionality available via arguments)
