fix(build): add ocamlformat dep so dune build @fmt has the binary

dune build @fmt was failing with 'Program ocamlformat not found in the
tree or in PATH'. Added ocamlformat as a with-test dep in dune-project
and opam.

Signed-off-by: Jonathan D.A. Jewell <6759885+hyperpolymath@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Jonathan D.A. Jewell <6759885+hyperpolymath@users.noreply.github.com>

Author: hyperpolymath

affinescript.opam

@@ -36,6 +36,7 @@ depends: [
   "odoc" {>= "2.4" & with-doc}
   "js_of_ocaml" {>= "5.0"}
   "js_of_ocaml-ppx" {>= "5.0"}
+  "ocamlformat" {>= "0.26" & with-test}
 ]
 build: [
   ["dune" "subst"] {dev}