Replace separate strlen(buffer) calls with the length returned directly by sprintf in both
num_toString and range_toString native functions. This avoids an unnecessary pass over the
formatted string buffer, improving performance for these hot-path number and range conversions.
Remove separate heap allocation for string text by storing it directly in the ObjString struct using a C99 flexible array member. This eliminates the need for an extra pointer indirection and a separate memory allocation call in wrenNewUninitializedString, while also simplifying the cleanup logic in wrenFreeObj by removing the explicit deallocation of the string's value buffer.
Evan Shaw