fix(Rect): fixes underflow in the Rect::intersection method

[Valentin271]

From @bugnano in #677

The Rect.intersection method contained the simple - operator, which panics on underflow.
This is strange, as all the other methods in Rect use saturating_add and saturating_sub.
So I changed the - operation to a saturating_sub, so that Rect.intersection never panics.

With a signed commit and a unit test.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2a87251) 90.9% compared to head (604d9d4) 90.9%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #678   +/-   ##
=====================================
  Coverage   90.9%   90.9%           
=====================================
  Files         42      42           
  Lines      12671   12678    +7     
=====================================
+ Hits       11519   11526    +7     
  Misses      1152    1152           

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[orhun]

Not sure if we need more unit tests for this, let's wait for review from other maintainers.

[joshka]

Seems like enough tests to me