Catch missing "v" in version constraints for dependencies

[punchagan]

Often, opam files are missing the v prefix for some of the package dependencies.

See, for instance:

• Fix base's upper bound on sexplib0 ocaml/opam-repository#25798
• liquid_*.0.1.2 missing v bounds ocaml/opam-repository#28225
• Apron bounds missing a v in apronext, goblint, and mopsa ocaml/opam-repository#28224
• Zarith_stubs_js missing v bounds ocaml/opam-repository#28227
• Patch catala, forester, and mutaml to use ppx_yojson_conv's v-prefixed version scheme ocaml/opam-repository#28182

@jmid also thinks it would be a good idea to have this as a lint check. See comment

jmid: Could it be as simple as "check first character in bound for a matching first character in a release"? 🤔

[jmid]

This is probably going to be a bit more complex than I initially thought... 🤷

For example, the opam repo still offers a mix of v-prefixed versions of apron as well as some older, date-based ones, which are still referred to, e.g.:

packages/mlgmpidl/mlgmpidl.1.2.8/opam:  "apron" {= "20140725"}
packages/mlgmpidl/mlgmpidl.1.2.8/opam:  "apron" {= "20150518"}
packages/bddapron/bddapron.2.3.2/opam:  "apron" {>= "20151015"}
packages/bddapron/bddapron.2.3.3/opam:  "apron"      {>= "20151015"}

Simultaneously there are other packages that have moved from a non-v-prefixed naming scheme to a v-prefixed one,
with only v-prefixed versions remaining on the main opam-repo, yet with earlier versions still being referred to, e.g.:

packages/nocrypto/nocrypto.0.5.4-2/opam:  "ppx_sexp_conv" {>= "113.33.01" & != "v0.11.0"}
packages/bistro/bistro.0.5.0/opam:  "sexplib" {>= "113.24.00" & < "v0.13"}
packages/protocol-9p-unix/protocol-9p-unix.2.0.2/opam:  "sexplib" {> "113.00.00"}
packages/protocol-9p/protocol-9p.2.0.2/opam:  "sexplib" {> "113.00.00" & < "v0.15"}
packages/odoc/odoc.1.5.3/opam:  "sexplib" {dev & >= "113.33.00" & with-test}
packages/vmnet/vmnet.1.5.1/opam:  "sexplib" {>= "113.24.00"}