fix(lint): resolve E415 in ocaml-agent, fix doc style in kdf/scrypt

Add pp pretty-printers to Config and Runtime_config modules to satisfy
E415 missing pretty-printer lint rule. Fix trailing period in scrypt.mli
doc comment.

scrypt/scrypt.mli

···
     [dk_len] octets. [n], the cost parameter, must be larger than 1 and a power
     of 2. [p], the parallelization parameter, must be a possitive integer and
     less than or equal to 2^32 - 1 / (4 * r)
-    @raise Invalid_argument when either [n], [p] or [dk_len] are not valid *)
+    @raise Invalid_argument when either [n], [p] or [dk_len] are not valid. *)