feat(license): SPDX Headers

[nothingismagick]

This PR is a first pass at applying SPDX license headers across all crates, node modules and workflow files. License headers are seen as a requirement in many FLOSS projects, and we want to be not only compliant, but show the way forward. We are using a rust nightly fmt feature to verify that all rust code has the appropriate license header.

This PR also attempts to cleanup some variations across Cargo.toml files.

Edit: While doing this, it became clear to me that we also need to claim copyright (for MIT purposes), which is why the license and copyright header is being changed to reference Tauri's status within the Commons Conservancy programme .

https://spdx.dev

What kind of change does this PR introduce? (check at least one)

• Other, please describe:
  License Headers and License Check

Does this PR introduce a breaking change? (check one)

• No

The PR fulfills these requirements:

• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.