Update contract licenses to MIT

[jacque006]

What is this PR doing?

• Update SPDX-License-Identifier contract license metadata from Unlicense to MIT for consistency with rest of repo.
• No other non-MIT license references were discovered

How can these changes be manually tested?

:eyes: , :judge:

Does this PR resolve or contribute to any issues?

Resolves https://github.com/getwax/bls-wallet/issues/607

Checklist

~I have manually tested these changes~ No testing needed

• [x] Post a link to the PR in the group chat

Guidelines

• If your PR is not ready, mark it as a draft
• The resolve conversation button is for reviewers, not authors
  • (But add a 'done' comment or similar)

[jacque006]

Updating the SPDX-License-Identifier appears to have changed the contract bytecode. This will have conflicts with https://github.com/getwax/bls-wallet/pull/606/ depending on which goes in first (deps.ts, package.jsons, etc.)

[jacque006]

@JohnGuilding ~That clients version was pinned to an experimental release in main when I started this work. It doesn't seem to be causing any harm so I rolled with it.~

~When we pin v1, we can set it back to a non-experimental semver.~ Set it back in this PR