ICM: Open-source AvalancheICTTRouter contracts

[Nuttymoon]

Some clean-up needs to be done once the audit is finished:

• Move the contracts dir content to the root path for better DX
• Change license to MIT (+ uniformize SPDX headers)
• Add the finalized audit to the repository
• Update the READMEs (Teleporter: Update READMEs #17)
• Use constant variables in tests to reduce build times (currently forge build takes up to 5min which is a very bad DX)
• Rename "Teleporter" to "ICM" (actually not sure we should do that now, waiting for Rename To ICM ava-labs/icm-contracts#652 is probably best)
• Update dependencies: use icm-contracts (instead of teleporter) and remove avalanche-interchain-token-transfer (that has been archived)