check: compare variadic fn params at the declared element type

installparams normalizes a decl's `T...` param lhs to []T in place
(cstage instead sets the resolved tp->type and never mutates AST), so
typeeqast compared a decl-synthesized fn type's []i64 against a fn
TYPE expr's surface i64 and confidently rejected
`let f: fn(args: i64...) void = sum;` — cstage accepts and runs. The
normalization wrapper now carries an op marker and typeeqast peels
exactly it, so both sides compare at the declared element type without
admitting genuinely different element depths. Fixture fnptrlet_variadic;
corpus pin 1486/2972.

docs/test-system-v2.md

@@ -32,9 +32,9 @@ categories out of the ordinary developer target.
 | Fixed point and self-host | `test-bootstrap` |
 | Host linker/platform behavior | `test-platform` |
 
-The live declarative compiler corpus has 1,485 fixtures and 2,970 C/WW cells:
+The live declarative compiler corpus has 1,486 fixtures and 2,972 C/WW cells:
 338 expected rejections (314 shared and 24 stage-specific), 17 compile-only
-successes, 191 exit-zero programs, and 939 explicit-exit programs.
+successes, 191 exit-zero programs, and 940 explicit-exit programs.
 
 147 native C carriers remain. They are partitioned exactly once as five
 in-process units, 24 byte/artifact gates, six bootstrap gates, one platform