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/thin_client.rs

@@ -11,7 +11,7 @@ use solana_sdk::{
     client::{AsyncClient, Client, SyncClient},
     clock::MAX_PROCESSING_AGE,
     commitment_config::CommitmentConfig,
-    fee_calculator::FeeCalculator,
+    fee_calculator::{FeeCalculator, FeeRateGovernor},
     hash::Hash,
     instruction::Instruction,
     message::Message,
@@ -445,6 +445,11 @@ impl SyncClient for ThinClient {
         }
     }
 
+    fn get_fee_rate_governor(&self) -> TransportResult<FeeRateGovernor> {
+        let fee_rate_governor = self.rpc_client().get_fee_rate_governor()?;
+        Ok(fee_rate_governor.value)
+    }
+
     fn get_signature_status(
         &self,
         signature: &Signature,