Fix LineFloat to store coordinates as float instead of double (#89)

[pangwangshu]

Problem

LineFloat was declaring its x1, y1, x2, y2 fields (and constructor/factory parameters) as double instead of float, defeating the purpose of having a separate float-precision Line implementation alongside LineDouble.

Fixes #89

Changes

• Changed LineFloat's fields, private constructor, and create() factory method to use float instead of double for coordinates (LineFloat.java)
• Added tests verifying:
  • LineFloat fields are declared as float while LineDouble fields remain double (via reflection)
  • Geometries.line(...) created from float coordinates reports isDoublePrecision() == false, and from double coordinates reports true

Test plan

• mvn test passes, including new LineTest cases