chore(tooling): add tox.ini migration stub

Provide a tox.ini that prints migration messages directing users to the
equivalent just recipes. Helps contributors still using muscle-memory
`tox -e py3` commands discover the new workflow.

Author: danceratopz

tox.ini

@@ -0,0 +1,85 @@
+# Migration stub: execution-specs now uses just (https://just.systems)
+# Install just: https://just.systems/man/en/pre-built-binaries.html
+#
+# Run `just` to see all available recipes.
+
+[tox]
+envlist = py3
+
+[testenv]
+allowlist_externals = printf, false
+skip_install = true
+deps =
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  Run \033[1m"just"\033[0m to see all available recipes.\n\n'
+    false
+
+[testenv:py3]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust fill\033[0m\n\n'
+    false
+
+[testenv:pypy3]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust fill-pypy\033[0m\n\n'
+    false
+
+[testenv:json_loader]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust json-loader\033[0m\n\n'
+    false
+
+[testenv:static]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust static\033[0m\n\n'
+    false
+
+[testenv:tests_pytest_py3]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust test-tests\033[0m\n\n'
+    false
+
+[testenv:tests_pytest_pypy3]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust test-tests-pypy\033[0m\n\n'
+    false
+
+[testenv:tests_benchmark_pytest_py3]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust test-tests-bench\033[0m\n\n'
+    false
+
+[testenv:benchmark-gas-values]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust bench-gas\033[0m\n\n'
+    false
+
+[testenv:benchmark-fixed-opcode-cli]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust bench-opcode\033[0m\n\n'
+    false
+
+[testenv:benchmark-fixed-opcode-config]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust bench-opcode-config\033[0m\n\n'
+    false
+
+[testenv:spec-docs]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust spec-docs\033[0m\n\n'
+    false
+
+[testenv:mkdocs]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust docs\033[0m\n\n'
+    false
+
+[testenv:changelog]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust changelog\033[0m\n\n'
+    false
+
+[testenv:markdownlint]
+commands =
+    printf '\n\033[1m  execution-specs has migrated from tox to just.\033[0m\n  Install just: https://just.systems/man/en/pre-built-binaries.html\n\n  This tox env can be run using just via:\n    \033[1mjust lint-md\033[0m\n\n'
+    false