Fix return types of three module API declarations to match definitions (#4676)

`ValkeyModule_FreeModuleUser`, `ValkeyModule_ACLAddLogEntry` and
`ValkeyModule_ACLAddLogEntryByUserName` are declared in valkeymodule.h
as returning void, but the implementations (`VM_FreeModuleUser`,
`VM_ACLAddLogEntry`, `VM_ACLAddLogEntryByUserName`) return int, and the
latter two document `VALKEYMODULE_OK` / `VALKEYMODULE_ERR`. Modules
calling them through the API table therefore call an int function via a
void function pointer, which is undefined behavior in C. On x86-64 and
arm64 the discarded return register makes it harmless in practice; on a
target with strict indirect-call signature checking (WebAssembly) the
call traps.

Declare them as int to match the implementation. Existing modules that
ignore the return value are unaffected; modules can now check the result
of the ACL log calls as documented. Also document that `FreeModuleUser`
returns `VALKEYMODULE_OK`.

Found by compiling the server with Emscripten, where
`redis.acl_check_cmd` in a Lua script (which calls `FreeModuleUser`
through the API table) trapped with 'null function or function signature
mismatch'.

Signed-off-by: Rain Valentine <rsg000@gmail.com>