add aurweb.time module

This module includes timezone-based utilities for a FastAPI request.
This commit introduces use of the AURTZ cookie within get_request_timezone.
This cookie should be set to the user or session's timezone.

* `make_context` has been modified to parse the request's timezone
  and include the "timezone" and "timezones" variables, along with
  a timezone specified "now" date.
+ Added `Timezone` attribute to aurweb.testing.requests.Request.user.

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_time.py

@@ -0,0 +1,33 @@
+import aurweb.config
+
+from aurweb.testing.requests import Request
+from aurweb.time import get_request_timezone, tz_offset
+
+
+def test_tz_offset_utc():
+    offset = tz_offset("UTC")
+    assert offset == "+00:00"
+
+
+def test_tz_offset_mst():
+    offset = tz_offset("MST")
+    assert offset == "-07:00"
+
+
+def test_request_timezone():
+    request = Request()
+    tz = get_request_timezone(request)
+    assert tz == aurweb.config.get("options", "default_timezone")
+
+
+def test_authenticated_request_timezone():
+    # Modify a fake request to be authenticated with the
+    # America/Los_Angeles timezone.
+    request = Request()
+    request.user.authenticated = True
+    request.user.Timezone = "America/Los_Angeles"
+
+    # Get the request's timezone, it should be America/Los_Angeles.
+    tz = get_request_timezone(request)
+    assert tz == request.user.Timezone
+    assert tz == "America/Los_Angeles"