Split signature throughput tracking out of FeeCalculator (#8447)

* 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

client/src/rpc_response.rs

@@ -4,7 +4,7 @@ use jsonrpc_core::Result as JsonResult;
 use solana_sdk::{
     account::Account,
     clock::{Epoch, Slot},
-    fee_calculator::FeeCalculator,
+    fee_calculator::{FeeCalculator, FeeRateGovernor},
     message::MessageHeader,
     pubkey::Pubkey,
     transaction::{Result, Transaction},
@@ -152,6 +152,12 @@ pub struct RpcBlockhashFeeCalculator {
     pub fee_calculator: FeeCalculator,
 }
 
+#[derive(Serialize, Deserialize, Clone, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct RpcFeeRateGovernor {
+    pub fee_rate_governor: FeeRateGovernor,
+}
+
 #[derive(Serialize, Deserialize, Clone, Debug)]
 #[serde(rename_all = "camelCase")]
 pub struct RpcKeyedAccount {