OCaml 5.2 support

[kit-ty-kate]

OCaml 5.2 added support for float16 bigarrays and owl-base fails with:

#=== ERROR while compiling owl-base.1.1 =======================================#
# context              2.2.0~beta2~dev | linux/x86_64 | ocaml-variants.5.2.0+trunk | file:///home/opam/opam-repository
# path                 ~/.opam/5.2/.opam-switch/build/owl-base.1.1
# command              ~/.opam/5.2/bin/dune build -p owl-base -j 1
# exit-code            1
# env-file             ~/.opam/log/owl-base-19-47ea7a.env
# output-file          ~/.opam/log/owl-base-19-47ea7a.out
### output ###
# (cd _build/default && /home/opam/.opam/5.2/bin/ocamlc.opt -w -40 -g -bin-annot -I src/base/.owl_base.objs/byte -I /home/opam/.opam/5.2/lib/ocaml/unix -no-alias-deps -o src/base/.owl_base.objs/byte/owl_utils_ndarray.cmo -c -impl src/base/owl_utils_ndarray.ml)
# File "src/base/misc/owl_utils_ndarray.ml", lines 9-22, characters 56-87:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# 
# File "src/base/misc/owl_utils_ndarray.ml", lines 26-41, characters 56-86:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# (cd _build/default && /home/opam/.opam/5.2/bin/ocamlc.opt -w -40 -g -bin-annot -I src/base/.owl_base.objs/byte -I /home/opam/.opam/5.2/lib/ocaml/unix -intf-suffix .ml -no-alias-deps -o src/base/.owl_base.objs/byte/owl_const.cmo -c -impl src/base/owl_const.ml)
# File "src/base/core/owl_const.ml", lines 48-61, characters 40-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# 
# File "src/base/core/owl_const.ml", lines 64-77, characters 39-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# 
# File "src/base/core/owl_const.ml", lines 80-93, characters 43-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# (cd _build/default && /home/opam/.opam/5.2/bin/ocamlopt.opt -w -40 -g -I src/base/.owl_base.objs/byte -I src/base/.owl_base.objs/native -I /home/opam/.opam/5.2/lib/ocaml/unix -intf-suffix .ml -no-alias-deps -o src/base/.owl_base.objs/native/owl_const.cmx -c -impl src/base/owl_const.ml)
# File "src/base/core/owl_const.ml", lines 48-61, characters 40-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# 
# File "src/base/core/owl_const.ml", lines 64-77, characters 39-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16
# 
# File "src/base/core/owl_const.ml", lines 80-93, characters 43-28:
# Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
# Here is an example of a case that is not matched:
# Float16