Fix Github actions build issues

[ethanbb]

I'm attempting to fix 3 completely different issues that are preventing tests from running:

• On linux pip, when installing caiman, pip install -r requirements.txt is failing because caiman no longer has a requirements.txt file. It shouldn't be necessary with all the dependencies listed in pyproject.toml now. However, this will still fail until Add versions to pyproject.toml flatironinstitute/CaImAn#1474 makes its way to main.
• On linux conda, there is a permissions error for the conda cache when installing mesmerize-core. Copilot suggested setting the cache dir manually instead of using the default.
• On macos conda, it seems the issue is related to the runner not having bundled conda due to being on ARM/Apple silicon architecture (Github-hosted runners for OSX no longer carry a bundled conda installation conda-incubator/setup-miniconda#344). The latest suggestion there is to specify the architecture manually as x64.