Migrate project licensing from MIT to Apache-2.0

[Copilot]

This updates UNsim’s licensing to Apache License 2.0 to align with the requested third-party usage posture, including patent grant coverage. The change is scoped to legal text and license metadata/documentation consistency.

• License text

  • Replaced LICENSE contents with the complete Apache License 2.0 text, including the appendix section.

• Package metadata

  • Updated project license metadata in pyproject.toml to SPDX identifier Apache-2.0.

• Documentation alignment

  • Updated README “Terms of Use & License” wording to reference Apache 2.0 and defer exact obligations to LICENSE.

# pyproject.toml
[project]
license = "Apache-2.0"

• Fixes change licence to Apache 2.0 #20