check: over-strict-mode lint (iter 19a)

When a fn-param is annotated (own T) but the body never consumes
it (consume_count == 0) and never destructures it via match, the
linearity pass now emits a Severity::Warning diagnostic with a
form-A-rendered (borrow T) rewrite as suggested_rewrite. Pure
advisory, Decision 10 unchanged.

First Warning-severity diagnostic the typechecker emits; three
CLI exit paths gated on Error-only.

JOURNAL: design entry + iter 19a shipping entry.

crates/ailang-surface/src/lib.rs

@@ -36,4 +36,4 @@ pub mod parse;
 pub mod print;
 
 pub use parse::{parse, parse_term, ParseError};
-pub use print::{print, term_to_form_a};
+pub use print::{print, term_to_form_a, type_to_form_a};