feat(v2): Compile-time required constraints for AnchorAccount

[chop0]

Custom AnchorAccount types can now declare a type-level list of AccountConstraint markers that every #[account(...)] usage must apply. The derive macro emits a const-block superset assertion per field; missing required constraints fail to compile.

• traits.rs: ConstraintList, Find<C, Idx> (frunk Here/There index trick), IsSuperset<R, I>, plus required_constraints![] helper macro.
• AnchorAccount gains type RequiredConstraints: ConstraintList. Built-in wrappers default to (); Box forwards from inner T.
• derive: per-field assertion built from attrs.namespaced and spliced beside the impl TryAccounts block.
• tests-v2/programs/custom-constraints: TestAccount (1 required) and TestMultiAccount (2 required) wrappers + handlers covering single, multi (reverse-order), Box forwarding, update(...) satisfaction.
• tests-v2/tests/ui_required_constraints: trybuild compile-fail snapshots for missing and partial requirements.

[vercel]

@chop0 is attempting to deploy a commit to the Solana Foundation Team on Vercel.

A member of the Team first needs to authorize it.

[jamie-osec]

Can you fix the compile-fail test issues?

[eteen12]

@chop0 id be happy to help with the compile tests if you want, i saw in the discord u were gonna take a look this morning, but if you want me to help out let me know