[Tests] Stabilize floating-point geometry assertions

[NachoSoto]

Summary

• replace exact CGRect equality with component-wise closeness checks in the four randomized aspect-preserving scale tests
• keep true identity-path assertions exact
• centralize the approximate rectangle assertions in a small test helper that preserves call-site file and line reporting

Root cause

The randomized tests derive a canvas size with floating-point multiplication, then the production calculation may recompute the same geometry through division and multiplication. Mathematically equivalent results can therefore differ by a few quadrillionths—for example an origin of 7.1e-15 instead of zero—without indicating a rendering bug.

Validation

• ImageInflaterRendererSpec repeated 50 times: 1,150 tests passed
• full iOS suite: 60 tests passed
• swiftlint --config .swiftlint.yml --strict: 0 violations