Only read text files that look like entries when opening folder journal (#1697)

* Add text file that should be ignored to basic test folder journal. Makes tons of tests fail
* Add additional files that should be ignored by FolderJournal
* Ignore all files in folder journal except year/month/day.txt
* Completely remake get_files in FolderJournal:
- move get_files into FolderJournal class and add underscore prefix
- create iterables to get for year/month folders and day files
- make year/month/day file reading strict: only exact expected months and days out of all possible months and days
* Restore accidentally-deleted self.sort() line
* Use match instead of string comparison to be os-agnostic
* Explicitly declare static methods
* Filter with glob first for max performance
* Explicitly check for valid dates in FolderJournal and add unit test
* Remove unneeded jrnl import
* Clean up method comment and add type hints
* Add is_valid_date unit test
* Elucidate comment

Co-authored-by: Jonathan Wren <jonathan@nowandwren.com>

tests/unit/test_time.py

@@ -3,6 +3,8 @@
 
 import datetime
 
+import pytest
+
 from jrnl import time
 
 
@@ -20,3 +22,23 @@ def test_default_minute_is_added():
         default_minute=30,
         bracketed=False,
     ) == datetime.datetime(2020, 6, 20, 0, 30)
+
+
+@pytest.mark.parametrize(
+    "inputs",
+    [
+        [2000, 2, 29, True],
+        [2023, 1, 0, False],
+        [2023, 1, 1, True],
+        [2023, 4, 31, False],
+        [2023, 12, 31, True],
+        [2023, 12, 32, False],
+        [2023, 13, 1, False],
+        [2100, 2, 27, True],
+        [2100, 2, 28, True],
+        [2100, 2, 29, False],
+    ],
+)
+def test_is_valid_date(inputs):
+    year, month, day, expected_result = inputs
+    assert time.is_valid_date(year, month, day) == expected_result