REF: Separate timezone-conversion from tslibs.conversion (#25938)

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -31,8 +31,8 @@ from pandas._libs.tslibs.timedeltas cimport cast_from_unit
 from pandas._libs.tslibs.timezones cimport is_utc, is_tzlocal, get_dst_info
 from pandas._libs.tslibs.timezones import UTC
 from pandas._libs.tslibs.conversion cimport (
-    tz_convert_single, _TSObject, convert_datetime_to_tsobject,
-    get_datetime64_nanos, tz_convert_utc_to_tzlocal)
+    _TSObject, convert_datetime_to_tsobject,
+    get_datetime64_nanos)
 
 # many modules still look for NaT and iNaT here despite them not being needed
 from pandas._libs.tslibs.nattype import nat_strings, iNaT  # noqa:F821
@@ -44,6 +44,9 @@ from pandas._libs.tslibs.offsets cimport to_offset
 from pandas._libs.tslibs.timestamps cimport create_timestamp_from_ts
 from pandas._libs.tslibs.timestamps import Timestamp
 
+from pandas._libs.tslibs.tzconversion cimport (
+    tz_convert_single, tz_convert_utc_to_tzlocal)
+
 
 cdef inline object create_datetime_from_ts(
         int64_t value, npy_datetimestruct dts,

pandas/_libs/tslibs/__init__.py

@@ -1,9 +1,10 @@
 # -*- coding: utf-8 -*-
 # flake8: noqa
 
-from .conversion import normalize_date, localize_pydatetime, tz_convert_single
+from .conversion import normalize_date, localize_pydatetime
 from .nattype import NaT, NaTType, iNaT, is_null_datetimelike
 from .np_datetime import OutOfBoundsDatetime
 from .period import Period, IncompatibleFrequency
 from .timestamps import Timestamp
 from .timedeltas import delta_to_nanoseconds, ints_to_pytimedelta, Timedelta
+from .tzconversion import tz_convert_single

pandas/_libs/tslibs/conversion.pxd

@@ -21,14 +21,10 @@ cdef convert_to_tsobject(object ts, object tz, object unit,
 cdef _TSObject convert_datetime_to_tsobject(datetime ts, object tz,
                                             int32_t nanos=*)
 
-cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2)
-
 cdef int64_t get_datetime64_nanos(object val) except? -1
 
 cpdef int64_t pydt_to_i8(object pydt) except? -1
 
 cdef maybe_datetimelike_to_i8(object val)
 
-cdef int64_t tz_convert_utc_to_tzlocal(int64_t utc_val, tzinfo tz)
-
 cpdef datetime localize_pydatetime(datetime dt, object tz)