- Adds support for Swift 6

- Migrates test suite to Swift Testing

Removes Gemfile

Updates for Xcode 16

Adds config for SPI DocC generation

Cleans up code in TrackGraphTests.swift

Adds creatorName to GPXExporter

Updates dependencies

Changes graph distance calcution when speed and date values are in th…

…e TrackPoints

Adds speed to TrackPoint

Updates README