lox-test-utils-v0.1.0-alpha.1

Added

• (lox-units) add Keplerian elements
• (lox-test-utils) add ApproxEq derive macro
• (lox-test-utils) add ApproxEq trait

Other

• add 3rd-party data licenses
• update SPDX headers and add helper script
• make Lox REUSE-compliant
• (lox-test-util) optimise and add docs
• get rid of float_eq and lox_math::is_close