Stop search after depth 1 if there is only one legal move

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% :warning:

Comparison is base (2511095) 92.71% compared to head (18517c9) 92.71%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #174 +/- ## ========================================== - Coverage 92.71% 92.71% -0.01% ========================================== Files 88 82 -6 Lines 13159 13149 -10 ========================================== - Hits 12201 12191 -10 Misses 958 958 ``` | [Files Changed](https://app.codecov.io/gh/FitzOReilly/fatalii/pull/174?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Heck) | Coverage Δ | | |---|---|---| | [eval/src/complex.rs](https://app.codecov.io/gh/FitzOReilly/fatalii/pull/174?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Heck#diff-ZXZhbC9zcmMvY29tcGxleC5ycw==) | `95.94% <100.00%> (ø)` | | | [search/src/alpha\_beta.rs](https://app.codecov.io/gh/FitzOReilly/fatalii/pull/174?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Heck#diff-c2VhcmNoL3NyYy9hbHBoYV9iZXRhLnJz) | `98.72% <100.00%> (+0.18%)` | :arrow_up: | ... and [11 files with indirect coverage changes](https://app.codecov.io/gh/FitzOReilly/fatalii/pull/174/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Heck)

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