Add option to not use cache xrfi.dpss_flagger

[tyler-a-cox]

By default, xrfi.dpss_flagger currently uses a cache to store intermediate filtering matrices, which speed up flagging. These matrices can get quite large, and if flagging patterns are different from antenna to antenna, the memory requirement of these functions could be high. By default, I've set the cache matrix to None in ant_class.auto_rfi_flagger and xrfi.dpss_flagger to decrease the memory requirement of those functions. Adding a cache does improve the performance of ant_class.auto_rfi_flagger though.

[codecov[bot]]

Codecov Report

Base: 97.04% // Head: 97.04% // No change to project coverage :thumbsup:

Coverage data is based on head (e973da1) compared to base (ec14f8e). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #432 +/- ## ======================================= Coverage 97.04% 97.04% ======================================= Files 9 9 Lines 3515 3515 ======================================= Hits 3411 3411 Misses 104 104 ``` | [Impacted Files](https://codecov.io/gh/HERA-Team/hera_qm/pull/432?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team) | Coverage Δ | | |---|---|---| | [hera\_qm/ant\_class.py](https://codecov.io/gh/HERA-Team/hera_qm/pull/432/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9xbS9hbnRfY2xhc3MucHk=) | `97.43% <ø> (ø)` | | | [hera\_qm/xrfi.py](https://codecov.io/gh/HERA-Team/hera_qm/pull/432/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#diff-aGVyYV9xbS94cmZpLnB5) | `99.59% <ø> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team)

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