fix: improve minimum zoom calculation in TileRanger

[razbroc]

This pull request makes a targeted improvement to the TileRanger class in src/geo/tileRanger.ts. The main change is a fix to how the minimum zoom level is calculated, particularly for edge cases where the bounding range width or height is zero. This prevents invalid or negative zoom levels and ensures the zoom does not exceed the current value.

Tile zoom calculation fix:

• Updated the calculation of minXZoom and minYZoom to handle cases where dx or dy are zero, defaulting to the current zoom value in those cases. Also, ensured that minZoom does not exceed the current zoom by including it in the Math.min call.

Question	Answer
Bug fix	✔

[vitaligi]

please add a test for the case when the input bbox generates a range with a single tile:
{minX: 0, maxX: 0, minY: 1, maxY: 1}