#### Summary of Changes
This PR implements the writer function for AccountMetaOptionalFields
in ByteBlockWriter::write_optional_fields().
#### Test Plan
Unit tests are included in this PR.
Tested in mnb w/ the prototype implementation of the tiered storage (#30626)
#### Summary of Changes
This PR introduces AccountMetaOptionalFields, the in-memory struct for
handling optional fields.
#### Test Plan
Unit tests are included in this PR.
Tested in mnb w/ the prototype implementation of the tiered storage (#30626).
* Makes Bank::load_program() return correct tombstones.
* Removes early TX failure caused by closed and invalid programs.
* Adjusts the feature gate of simplify_writable_program_account_check.
#### Problem
AccountMetaFlags and its fields are required to be public as the visibility of their get
functions generated by `bit_fields` are tied to the visibility of their fields, and the
get functions will later be used to support the TieredAccountMeta for AccountMeta.
#### Summary of Changes
Make AccountMetaFlags and its fields public
#### Summary of Changes
This PR adds raw_len() to ByteBlockWriter which returns
the length of the data after decoding. This information is needed
for the cold storage to keep track of the current size of the account
block after decompression.
#### Test Plan
Improved existing tests to verify the returned raw_len().
Tested in mnb w/ the prototype implementation of the tiered storage (https://github.com/solana-labs/solana/pull/30626)
`Arc` is already a reference internally, so it does not seem to be
beneficial to pass a reference to it. Just adds an extra layer of
indirection.
Functions that need to be able to increment `Arc` reference count need
to take `Arc<AtomicBool>`, but those that just want to read the
`AtomicBool` value can accept `&AtomicBool`, making them a bit more
generic.
This change focuses specifically on `Arc<AtomicBool>`. There are other
uses of `&Arc<T>` in the code base that could be converted in a similar
manner. But it would make the change even larger.
#### 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
Support Lz4 in ByteBlockWriter.
#### Test Plan
Added test cases for Lz4.
Tested in mnb w/ the prototype implementation of the tiered storage (#30626)
The callstack updated in this PR passed an &Arc<...> down only to have
the bottom level clone the reference. Thus, we are giving shared
ownership so the reference is a bit redundant and arguably obscures the
intention to clone further down the callstack.
#### 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.
#### Problem
AppendVec currently uses std::io::ErrorKind::Other for its own errors.
#### Summary of Changes
This PR introduces AppendVecError and has AppendVec use it.
Jeff Washington (jwash)
Andrew Fitzgerald
Brooks
Yueh-Hsuan Chiang
steviez
Tao Zhu
Alexander Meißner
Pankaj Garg
Illia Bobyr