#### Problem
There's no way to get incremental snapshot information from RPC.
#### Summary of Changes
- Add new RPC method, `getHighestSnapshotSlot` that returns a `SnapshotSlotInfo`, which contains both the highest full snapshot slot, and the highest incremental snapshot slot _based on_ the full snapshot.
- Deprecate old RPC method, `getSnapshotSlot`
- Update API docs
Fixes#19579
* feat: introduce get_inflation_reward rpc call
* fix: style suggestions
* fix: more style changes and match how other rpc functions are defined
* feat: get reward for a single epoch
* feat: default to the most recent epoch
* fix: don't factor out get_confirmed_block
* style: introduce from impl for RpcEncodingConfigWrapper
* style: bring commitment into variable
* feat: support multiple pubkeys for get_inflation_reward
* feat: add get_inflation_reward to rpc client
* feat: return rewards in order
* fix: rename pubkeys to addresses
* docs: introduce jsonrpc docs for get_inflation_reward
* style: early return in map (not sure which is more idiomatic)
* fix: call the rpc client function args addresses as well
* fix: style
* fix: filter out only addresses we care about
* style: make this more idiomatic
* fix: change rpc client epoch to optional and include some docs edits
* feat: filter out rent rewards in get_inflation_reward
* feat: add option epoch config param to get_inflation_reward
* feat: rpc client get_inflation_reward takes epoch instead of config and some filter staking and voting rewards
* Add rpc_client api for getRecentPerformanceSamples
* Prep fn for variable avg slot time
* Use recent-perf-samples to more-accurately estimate epoch completed times
* Spell out average
* Deprecate commitment variants
* Add new CommitmentConfig builders
* Add helpers to avoid allowing deprecated variants
* Remove deprecated transaction-status code
* Include new commitment variants in runtime commitment; allow deprecated as long as old variants persist
* Remove deprecated banks code
* Remove deprecated variants in core; allow deprecated in rpc/rpc-subscriptions for now
* Heavier hand with rpc/rpc-subscription commitment
* Remove deprecated variants from local-cluster
* Remove deprecated variants from various tools
* Remove deprecated variants from validator
* Update docs
* Remove deprecated client code
* Add new variants to cli; remove deprecated variants as possible
* Don't send new commitment variants to old clusters
* Retain deprecated method in test_validator_saves_tower
* Fix clippy matches! suggestion for BPF solana-sdk legacy compile test
* Refactor node version check to handle commitment variants and transaction encoding
* Hide deprecated variants from cli help
* Add cli App comments
* Add rpc endpoint to return the state of multiple accounts from the same bank
* Add docs
* Review comments: Dedupe account code, default to base64, add max const
* Add get_multiple_accounts to rpc-client