core/ci: fix windows-specific issues

- use portable separators
- paths should be prepended with r' (so backwards slash isn't treated as escaping)
- sqlite connections should be closed (otherwise windows fails to remove the underlying db file)
- workaround for emojis via PYTHONUTF8=1 test for now
- make ZipPath portable
- properly use tox python environment everywhere

  this was causing issues on Windows
  e.g.
      WARNING: test command found but not installed in testenv
        cmd: C:\hostedtoolcache\windows\Python\3.9.12\x64\python3.EXE

tox.ini

@@ -12,7 +12,7 @@ passenv = CI CI_*
 [testenv:tests-core]
 commands =
     pip install -e .[testing]
-    python3 -m pytest \
+    {envpython} -m pytest \
                       tests/core.py      \
                       tests/sqlite.py    \
                       tests/get_files.py \
@@ -29,7 +29,7 @@ commands =
 
     # installed to test my.core.serialize while using simplejson and not orjson
     pip install simplejson
-    python3 -m pytest \
+    {envpython} -m pytest \
                       tests/serialize_simplejson.py \
                       {posargs}
 
@@ -52,28 +52,28 @@ commands =
 
     hpi module install my.reddit.rexport
 
-    python3 -m pytest tests \
+    {envpython} -m pytest tests \
             # ignore some tests which might take a while to run on ci..
             --ignore tests/takeout.py        \
             --ignore tests/extra/polar.py \
             # dont run simplejson compatibility test since orjson is now installed
-            --ignore tests/serialize_simplejson.py
+            --ignore tests/serialize_simplejson.py \
             {posargs}
 
 
 [testenv:demo]
 commands =
     pip install git+https://github.com/karlicoss/hypexport
-    ./demo.py
+    {envpython} ./demo.py
 
 
 [testenv:mypy-core]
-whitelist_externals = cat
+allowlist_externals = cat
 commands =
     pip install -e .[testing,optional]
     pip install orgparse # used it core.orgmode?
     # todo add tests?
-    python3 -m mypy --install-types --non-interactive \
+    {envpython} -m mypy --install-types --non-interactive \
                     -p my.core \
                     --txt-report  .coverage.mypy-core \
                     --html-report .coverage.mypy-core \
@@ -109,7 +109,7 @@ commands =
 
     # todo fuck. -p my.github isn't checking the subpackages?? wtf...
     # guess it wants .pyi file??
-    python3 -m mypy --install-types --non-interactive \
+    {envpython} -m mypy --install-types --non-interactive \
                     -p my.browser                     \
                     -p my.endomondo                   \
                     -p my.github.ghexport             \