add spatial error and unit test cases

[ZoeJacky]

spatial error: the gap between the last point of the cursor movement path to the center of the target minus target radius. PS: when the gap <= target radius, spatial error = 0

[codecov[bot]]

Codecov Report

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

Comparison is base (96270c0) 90.01% compared to head (0269177) 90.09%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #255 +/- ## ========================================== + Coverage 90.01% 90.09% +0.08% ========================================== Files 19 19 Lines 1602 1615 +13 ========================================== + Hits 1442 1455 +13 Misses 160 160 ```

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[sonarcloud[bot]]

Quality Gate passed

The SonarCloud Quality Gate passed, but some issues were introduced.

1 New issue
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud