add x-quality metadata to 171 packages, fix sse build

Generate .opam.template files with x-quality-* fields based on
detected package features:
- x-quality-build: has lib/ with .ml files
- x-quality-test: has test/ with .ml files
- x-quality-fuzz: has fuzz/ with .ml files
- x-quality-interop: has test/interop/ directory
- x-quality-cram: has test/*.t/ directories

These fields are picked up by dune's opam generation and will be
checked by merlint E910 for consistency.

Also: add fmt dep to ocaml-sse/lib/dune (Fmt.pf used without dep).