[elixir] CI/CD pipeline

[fresh-borzoni]

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Description

depends on #452

Set up GitHub Actions for Elixir bindings: compile NIF, run tests (unit + integration with Docker cluster), build precompiled binaries for major platforms (linux x86_64/aarch64, macOS x86_64/aarch64), publish to Hex.

Willingness to contribute

• I'm willing to submit a PR!