#### Summary of Changes
This PR initiates the implementation of TieredAccountsFile::write_accounts,
which will later support AccountsFile::append_accounts.
This PR also introduces TieredAccountsFileWriter -- the main writer struct for a
TieredAccountsFile.
#### Test Plan
Extended existing unit tests.
#### Summary of Changes
This PR initiates the implementation of the main struct for the
tiered accounts storage --- TieredStorage. Specifically,
it defines the TieredStorage struct, TieredStorageFormat,
and skeleton implementation of new_writable().
#### Test Plan
Unit tests are included in this PR.
#### Summary of Changes
This PR implements AccountIndexFormat::AddressAndOffset, the index format
that will be used by the hot account storage.
#### Test Plan
Unit tests are included in this PR.
Tested via the prototype implementation of tiered-storage.
#### Summary of Changes
This PR introduces TieredReadableAccount, a struct that takes a generic
TieredAccountMeta that implements ReadableAccount and support
StoredAccountMeta.
#### Test Plan
More tests will be added once more reader and writer functions for hot
accounts have been added.
#### Summary of Changes
This PR introduces HotAccountMeta, the storage and in-memory struct of
the metadata struct for a hot account.
#### Test Plan
Unit tests are included in this PR.
Tested in mnb w/ the prototype implementation of the tiered account storage (#30626)
#### Summary of Changes
This PR implements AccountMetaFlags, which will later be used in
the tiered accounts storage to support optional fields.
#### Test Plan
Unit tests are included in this PR.
#### Summary of Changes
This PR includes the util structs for writing byte blocks, which will be used
by the TieredStorage writer (currently used in the prototype #30626).
The PR only includes the Raw encoding format. Will add more in subsequent PRs.
#### Test Plan
Tested in mnb with the prototype implementation of the tiered-storage (#30626)
Unit tests are also included in this PR.
#### Summary of Changes
This PR includes the implementation of the footer for the tiered account storage.
Tiered account storage proposal: #30551
The prototype implementation of the tiered account storage: #30626.
Yueh-Hsuan Chiang