Phase 120: Complete boolean return type conversions

Converted 4 remaining predicate functions from int to bool:
- iscleared() (gc_weak.cpp:52) - GC weak table predicate
- isneg() (lobject.cpp:207) - Sign checking predicate
- rawfinishnodeset() (ltable.cpp:1187) - Table insertion success check
- checkbuffer() (lzio.cpp:46) - Buffer validation predicate

Also updated call site in Table::setInt() to use bool variable.

This completes the boolean modernization initiative started in
Phases 113 and 117, bringing total bool conversions to 16 functions.

Testing:
- All tests pass (final OK !!!)
- Performance: 4.45s avg (within acceptable bounds)

Follows pattern from Phase 117 (5 predicates) and Phase 113 (7 predicates).

Author: claude

src/memory/gc/gc_weak.cpp

@@ -49,11 +49,11 @@
 ** For other objects: if really collected, cannot keep them; for objects
 ** being finalized, keep them in keys, but not in values.
 */
-static int iscleared(global_State* g, const GCObject* o) {
-    if (o == nullptr) return 0;  /* non-collectable value */
+static bool iscleared(global_State* g, const GCObject* o) {
+    if (o == nullptr) return false;  /* non-collectable value */
     else if (novariant(o->getType()) == LUA_TSTRING) {
         markobject(g, o);  /* strings are 'values', so are never weak */
-        return 0;
+        return false;
     }
     else return iswhite(o);
 }

src/objects/lobject.cpp

@@ -204,10 +204,10 @@ lu_byte luaO_hexavalue (int c) {
 }
 
 
-static int isneg (const char **s) {
-  if (**s == '-') { (*s)++; return 1; }
+static bool isneg (const char **s) {
+  if (**s == '-') { (*s)++; return true; }
   else if (**s == '+') (*s)++;
-  return 0;
+  return false;
 }
 
 

src/objects/ltable.cpp

@@ -1184,12 +1184,12 @@ static int finishnodeset (Table *t, TValue *slot, TValue *val) {
 }
 
 
-static int rawfinishnodeset (TValue *slot, TValue *val) {
+static bool rawfinishnodeset (TValue *slot, TValue *val) {
   if (isabstkey(slot))
-    return 0;  /* no slot with that key */
+    return false;  /* no slot with that key */
   else {
     *slot = *val;
-    return 1;  /* success */
+    return true;  /* success */
   }
 }
 
@@ -1522,7 +1522,7 @@ void Table::setInt(lua_State* L, lua_Integer key, TValue* value) {
   if (ik > 0)
     obj2arr(this, ik - 1, value);
   else {
-    int ok = rawfinishnodeset(getintfromhash(this, key), value);
+    bool ok = rawfinishnodeset(getintfromhash(this, key), value);
     if (!ok) {
       TValue k;
       setivalue(&k, key);

src/serialization/lzio.cpp

@@ -43,16 +43,16 @@ void luaZ_init (lua_State *L, ZIO *z, lua_Reader reader, void *data) {
 
 /* --------------------------------------------------------------- read --- */
 
-static int checkbuffer (ZIO *z) {
+static bool checkbuffer (ZIO *z) {
   if (z->n == 0) {  /* no bytes in buffer? */
     if (luaZ_fill(z) == EOZ)  /* try to read more */
-      return 0;  /* no more input */
+      return false;  /* no more input */
     else {
       z->n++;  /* luaZ_fill consumed first byte; put it back */
       z->p--;
     }
   }
-  return 1;  /* now buffer has something */
+  return true;  /* now buffer has something */
 }