PERF: fix regression in tz_convert_from_utc (#38074)

Author: lidavidm

pandas/_libs/tslibs/tzconversion.pyx

@@ -426,7 +426,7 @@ def tz_convert_from_utc(const int64_t[:] vals, tzinfo tz):
     int64 ndarray of converted
     """
     cdef:
-        int64_t[:] converted
+        const int64_t[:] converted
 
     if len(vals) == 0:
         return np.array([], dtype=np.int64)
@@ -437,7 +437,7 @@ def tz_convert_from_utc(const int64_t[:] vals, tzinfo tz):
 
 @cython.boundscheck(False)
 @cython.wraparound(False)
-cdef int64_t[:] _tz_convert_from_utc(const int64_t[:] vals, tzinfo tz):
+cdef const int64_t[:] _tz_convert_from_utc(const int64_t[:] vals, tzinfo tz):
     """
     Convert the given values (in i8) either to UTC or from UTC.
 
@@ -459,7 +459,7 @@ cdef int64_t[:] _tz_convert_from_utc(const int64_t[:] vals, tzinfo tz):
         str typ
 
     if is_utc(tz):
-        converted = vals.copy()
+        return vals
     elif is_tzlocal(tz):
         converted = np.empty(n, dtype=np.int64)
         for i in range(n):