[TieredStorage] TieredAccountMeta (1/N) (#32220)

#### Summary of Changes
This PR introduces TieredAccountMeta, a trait that allows different implementations
of the account meta for different tiers of the accounts storage.

This PR includes the mutator and getter methods for the common TieredAccountMeta
fields.  Functions that also work with the account data block will be in separate PRs.

runtime/src/tiered_storage/meta.rs

@@ -22,6 +22,53 @@ pub struct AccountMetaFlags {
     reserved: B29,
 }
 
+/// A trait that allows different implementations of the account meta that
+/// support different tiers of the accounts storage.
+pub trait TieredAccountMeta: Sized {
+    /// Constructs a TieredAcountMeta instance.
+    fn new() -> Self;
+
+    /// A builder function that initializes lamports.
+    fn with_lamports(self, lamports: u64) -> Self;
+
+    /// A builder function that initializes the number of padding bytes
+    /// for the account data associated with the current meta.
+    fn with_account_data_padding(self, padding: u8) -> Self;
+
+    /// A builder function that initializes the owner's index.
+    fn with_owner_index(self, index: u32) -> Self;
+
+    /// A builder function that initializes the account data size.
+    /// The size here represents the logical data size without compression.
+    fn with_data_size(self, data_size: u64) -> Self;
+
+    /// A builder function that initializes the AccountMetaFlags of the current
+    /// meta.
+    fn with_flags(self, flags: &AccountMetaFlags) -> Self;
+
+    /// Returns the balance of the lamports associated with the account.
+    fn lamports(&self) -> u64;
+
+    /// Returns the number of padding bytes for the associated account data
+    fn account_data_padding(&self) -> u8;
+
+    /// Returns the size of its account data if the current accout meta
+    /// shares its account block with other account meta entries.
+    ///
+    /// Otherwise, None will be returned.
+    fn data_size_for_shared_block(&self) -> Option<usize>;
+
+    /// Returns the index to the accounts' owner in the current AccountsFile.
+    fn owner_index(&self) -> u32;
+
+    /// Returns the AccountMetaFlags of the current meta.
+    fn flags(&self) -> &AccountMetaFlags;
+
+    /// Returns true if the TieredAccountMeta implementation supports multiple
+    /// accounts sharing one account block.
+    fn supports_shared_account_block() -> bool;
+}
+
 impl AccountMetaFlags {
     pub fn new_from(optional_fields: &AccountMetaOptionalFields) -> Self {
         let mut flags = AccountMetaFlags::default();