Stop requiring Reason for tests

[funwithcthulhu]

Summary

• remove reason from Dream's with-test dependencies
• keep the standalone r-* Reason examples out of the repository-wide Dune build
• make the CI example build select OCaml .ml entrypoints only

Notes

The Reason examples remain in the tree as standalone examples. This only removes the requirement that Dream's test dependency set and repository build compile them.

Relates to #420, specifically the question of forcing tests to compile Reason examples. It does not close the broader OCaml 5.5 / Lwt 6 tracking issue.

Validation

• git diff --check
• opam lint dream.opam
• opam lint --recursive example
• opam exec -- dune build --only-packages dream-pure,dream-httpaf,dream @install still fails locally because this switch is missing normal Dream dependencies, but the output no longer includes reason, refmt, or example/r-* traversal.