fix for half-space solution

[hvasbath]

• in case cosB is identical to zero, which would result in inf due to division by zero, cosB is set to machine number precision
• added test to compare to matlab solution

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.51 :tada:

Comparison is base (12b6ebe) 70.65% compared to head (18a80cf) 71.16%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #26 +/- ## ========================================== + Coverage 70.65% 71.16% +0.51% ========================================== Files 19 19 Lines 1179 1200 +21 ========================================== + Hits 833 854 +21 Misses 346 346 ``` | [Impacted Files](https://app.codecov.io/gh/tbenthompson/cutde/pull/26?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ben+Thompson) | Coverage Δ | | |---|---|---| | [tests/test\_tde.py](https://app.codecov.io/gh/tbenthompson/cutde/pull/26?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ben+Thompson#diff-dGVzdHMvdGVzdF90ZGUucHk=) | `99.04% <100.00%> (+0.10%)` | :arrow_up: |

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[tbenthompson]

Wonderful! Thank you!