License Change Notice: MIT → Apache License 2.0

[cbuahin]

The reasons for the switch:

1. Explicit patent protection. Apache 2.0 includes an explicit, irrevocable patent grant from every contributor, plus a patent retaliation clause. This protects everyone who uses this project — including commercial users — from patent claims related to contributed code. MIT has no equivalent language.
2. Attribution is easier to enforce. Apache 2.0 requires anyone who redistributes modified code to clearly state what they changed and to carry forward the project's NOTICE file. MIT only requires preserving the copyright notice. This gives contributors and the project stronger, clearer recognition when the code is reused or forked downstream.
3. Alignment with industry norms. Apache 2.0 is the standard license for large, widely adopted open-source infrastructure projects (Apache Foundation projects, most major cloud and data tooling, and much of the enterprise open-source ecosystem). Using it lowers legal review friction for organizations evaluating this project as a dependency.
4. No effect on our existing commitments. All prior and current contributors have signed the project's Contributor License Agreement, which already grants the project the right to relicense contributions. This change uses that existing right — it does not require, and has not required, retroactively altering anyone's original contribution terms.

See #122 for details.