Allow VariantData to take either a vcz path or the zarr store itself

[hyanwong]

Starts to address https://github.com/tskit-dev/tsinfer/issues/924

Changes are very minor: most of this is just in testing

[codecov[bot]]

Codecov Report

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

Project coverage is 93.17%. Comparing base (6c02f9d) to head (fe0b969). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #966 +/- ## ======================================= Coverage 93.16% 93.17% ======================================= Files 18 18 Lines 6337 6343 +6 Branches 1133 1134 +1 ======================================= + Hits 5904 5910 +6 Misses 294 294 Partials 139 139 ``` | [Flag](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/966/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | Coverage Δ | | |---|---|---| | [C](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/966/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `93.17% <100.00%> (+<0.01%)` | :arrow_up: | | [python](https://app.codecov.io/gh/tskit-dev/tsinfer/pull/966/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `95.54% <100.00%> (+<0.01%)` | :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=tskit-dev#carryforward-flags-in-the-pull-request-comment) to find out more.

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[benjeffery]

@mergifyio rebase

[mergify[bot]]

rebase

☑️ Nothing to do

- [ ] `-conflict` [📌 rebase requirement] - [X] `-closed` [📌 rebase requirement] - [X] `queue-position=-1` [📌 rebase requirement] - [X] any of: - [X] `#commits-behind>0` [📌 rebase requirement] - [X] `#commits>1` [📌 rebase requirement] - [ ] `-linear-history` [📌 rebase requirement]