lib: move all UNITTEST prototypes to C files

- make extract-unit-protos handle multi-line prototypes - but they need
  to be above the implementation

- Prototypes for static functions we use in unit tests should not be in
  header files. We generate lib/unitprotos.h for this purpose

- Removed some function wrappers written for unit tests and make them
  use UNITTEST function directly.

- Renamed time2str() in the tool to timebuf() since we have the same
  name in lib/ and in unit tests they can both be used non-static in a
  build.

This reverts commit f95fadd116.

Follow-up to #21010

Closes #21014

lib/uint-hash.c

@@ -181,7 +181,8 @@ void *Curl_uint32_hash_get(struct uint_hash *h, uint32_t id)
   return NULL;
 }
 
-static void uint_hash_clear(struct uint_hash *h)
+UNITTEST void uint_hash_clear(struct uint_hash *h);
+UNITTEST void uint_hash_clear(struct uint_hash *h)
 {
   if(h && h->table) {
     struct uint_hash_entry *he, **he_anchor;
@@ -198,13 +199,6 @@ static void uint_hash_clear(struct uint_hash *h)
   }
 }
 
-#ifdef UNITTESTS
-UNITTEST void Curl_uint32_hash_clear(struct uint_hash *h)
-{
-  uint_hash_clear(h);
-}
-#endif
-
 void Curl_uint32_hash_destroy(struct uint_hash *h)
 {
   DEBUGASSERT(h->init == CURL_UINT32_HASHINIT);