chore: make a couple more things frozen/hashable (#307)

Manifest and Fpath were not marked with the decorator to make frozen
dataclasses, so were unhashable in Python. This adds the decorator to
make them
hashable.

- [x] I ran `make setup && make` to update the generated code after
editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of
the CLI.
For example, the Semgrep backend need to still be able to *consume* data
generated
	  by Semgrep 1.17.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades

Co-authored-by: Yoann Padioleau <[email protected]>

semgrep_output_v1.atd

@@ -71,7 +71,7 @@ type raw_json <ocaml module="Yojson.Basic" t="t"> = abstract
 (*****************************************************************************)
 
 (* File path. less: could convert directly to Path class of pathlib library for Python *)
-type fpath <ocaml attr="deriving show"> = string wrap <ocaml module="ATD_string_wrap.Fpath">
+type fpath <ocaml attr="deriving show"> <python decorator="dataclass(frozen=True)">= string wrap <ocaml module="ATD_string_wrap.Fpath">
 
 type uri = string wrap <ocaml module="ATD_string_wrap.Uri">
 
@@ -1856,7 +1856,8 @@ type manifest_kind
     (* pyproject.toml - https://packaging.python.org/en/latest/guides/writing-pyproject-toml/ *)
 ]
 
-type manifest = {
+type manifest
+  <python decorator="dataclass(frozen=True)">   = {
   kind: manifest_kind;
   path: fpath;
 }