Fix some bugs from most recent PR

[daviesje]

This fixes two bugs which slipped through the tests when we removed recursion

• the hacky XraySourceBox construction has been changed to work with the new cached properties in the structs.
• HaloField required arrays have been updated

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 74.11%. Comparing base (add5314) to head (4071f4e). Report is 4 commits behind head on v4-prep.

Files with missing lines	Patch %	Lines
src/py21cmfast/drivers/single_field.py	0.00%	4 Missing :warning:
src/py21cmfast/wrapper/outputs.py	66.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## v4-prep #440 +/- ## =========================================== + Coverage 74.07% 74.11% +0.04% =========================================== Files 23 23 Lines 3745 3747 +2 Branches 639 641 +2 =========================================== + Hits 2774 2777 +3 + Misses 743 742 -1 Partials 228 228 ```

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