Migrate Python tests to Lua

[p0rtale]

Converted all Python-based tests to Lua except:

• test/test_probe_uri.py
• test/test_reload.py

[Copilot]

Pull Request Overview

This PR migrates existing Python tests to Lua, introduces new Lua integration tests, updates test helpers, and adjusts the CI pipeline to run Lua-based tests.

• Add comprehensive Lua integration tests covering synchronization, subscription, quitting/rejoining, payloads, clock skew, initialization flows, false rumors, encryption, dissemination, self-dead detection, broadcasting, and allowed-members filtering.
• Extend test helpers in server.lua, instance.lua, and cluster2.lua with new methods and refine startup/teardown logic.
• Update GitHub Actions workflow to install dependencies, set up Tarantool, run luacheck, build the project, and execute tests via luatest.

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test_lua/integration/*.lua	New Lua integration tests replacing Python ones
test_lua/helpers/server.lua	Added add_member, probe_uri, broadcast, etc. methods
test_lua/helpers/instance.lua	Adjust default WAL/vinyl directory defaults and grants
test_lua/helpers/cluster2.lua	Introduce hostname arg, port checks, environment vars
.github/workflows/test.yml	Switch to Lua setup, install rocks, run luacheck & luatest

[yngvar-antonsson]

Well done, @p0rtale ! Titanic work here. I've added a couple of notes.