Anchor v2 SPL account types and constraint markers.
Separate crate (like v1's anchor-spl) that provides zero-copy TokenAccount
and Mint types for use with Account<T>, plus namespaced constraint markers
for token::mint, token::authority, mint::decimals, etc.
The token CPI helpers intentionally accept either the Token Program or
Token-2022 for base token instructions. The token account types themselves
remain strict Token Program account layouts. For account validation that must
accept both Token and Token-2022 owners, use
anchor_lang::prelude::InterfaceAccount with the token_interface
module's token account types.