Clarify and Clean Up Unused Transaction Size & Block Transaction Constants

[raymondkfcheung]

pallet-transaction-storage defines several constants that appear unused or unclear in purpose:

/// Maximum bytes that can be stored in one transaction.
// TODO: find out what is "allocator" and "allocator limit"
// Setting higher limit also requires raising the allocator limit.
// TODO: not used, can we remove or use?
pub const DEFAULT_MAX_TRANSACTION_SIZE: u32 = 8 * 1024 * 1024;

// TODO: not used, can we remove or use?
pub const DEFAULT_MAX_BLOCK_TRANSACTIONS: u32 = 512;

Tasks:

• Determine the intended role of these defaults.
• Confirm whether they are actually used anywhere in the runtime or pallet logic.
• Clarify what “allocator” / “allocator limit” refers to and whether it constrains these values.
• Decide whether to remove them, replace them with configuration items, or integrate them properly.
• Update comments and code accordingly.

Related:

• https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/transaction-storage/src/lib.rs
• Align Types between Bulletin and SDK polkadot-sdk#10578 (comment)