Fix: intersect() drops Validated types when merging interface with extends

[nickpokhilko]

What

Add (Validated, Validated), (Validated, _) and (_, Validated) arms to intersect() in tsparser/src/parser/types/typ.rs.

Why

When resolving interface Derived extends Base, fields present in both interfaces with validators in the derived type (e.g. string & MinLen<1>) fell through all existing patterns to the catch-all (_, _) => Type::Basic(Basic::Never), silently erasing the field from the parsed schema.

Root cause path:

1. do_interface_decl intersects the derived interface body with each base type via intersect(derived, base)
2. For a field present in both, the derived field type is Validated { typ: Basic(String), expr: MinLen∧MaxLen } and the base is Basic(String)
3. intersect(Validated{…}, Basic(String)) matched none of the existing Validation/Validated arms (which only handle Validation — the unapplied expression type, not Validated — the already-applied wrapper)
4. Fell through to (_, _) => Type::Basic(Basic::Never)

Verification

Added tests/testdata/interface_extends_validation.txt covering:

• Single extends with MinLen/MaxLen validators on an inherited field
• Two levels of extends with optional validated fields

cargo test -p encore-tsparser test_parser passes.