Fix opening tiff and fits files

[TomNicholas]

@scottyhq this is the minimum needed for #160

• [x] Closes #160
• [x] Tests added
• [x] Tests passing
• [x] Full type hint coverage
• [x] Changes are documented in docs/releases.rst
• [ ] New functions/methods are listed in api.rst
• [ ] New functionality has documentation

[TomNicholas]

I found that passing a local filepath with no / anywhere exposes a bug in fsspec. I tried this out successfully on the same file you pointed me to @scottyhq but downloaded locally, and referred to as open_virtual_dataset("./lcmap_tiny_cog_2020.tif", filetype='tiff', indexes={}). I haven't tried it on the fits file yet (as I'm on a a train with spotty signal :grin:)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.43%. Comparing base (cc97112) to head (cb3f969). Report is 28 commits behind head on main.

:exclamation: Current head cb3f969 differs from pull request most recent head c705ce8

Please upload reports for the commit c705ce8 to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ========================================== + Coverage 91.38% 92.43% +1.05% ========================================== Files 20 20 Lines 1300 1521 +221 ========================================== + Hits 1188 1406 +218 - Misses 112 115 +3 ``` | [Flag](https://app.codecov.io/gh/zarr-developers/VirtualiZarr/pull/162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/zarr-developers/VirtualiZarr/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers) | `92.43% <100.00%> (+1.05%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zarr-developers#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.