Restructure: consolidate everything inside testium/ package

Move src/lib/ → src/testium/runtime/ (internal plumbing)
Move src/testium/libs/ → src/testium/api/ (public SDK for test scripts)
Move src/py_func/ → src/testium/py_func/ (Python subprocess)
Move src/lua_func/ → src/testium/lua_func/ (Lua subprocess data)

The package now ships as a single coherent unit instead of four sibling
top-level packages (testium, lib, py_func, lua_func) — pip install
gives a clean site-packages/testium/ with no namespace pollution; .lua
files travel with the wheel via package_data; the wheel installs
cleanly and `testium -b` runs end-to-end including py_func subprocesses
and entry-point exporter plugins.

Naming:
- runtime/ (internal, no API guarantees) clearer than lib/
- api/ (public SDK consumed as `import api.testium as tm`) clearer than libs/

Imports updated en masse: from lib. → from runtime. and from libs. →
from api., plus the importlib.import_module("libs.*") strings in
test_item_console.py and test_item_runtime_plot.py. Test/example
scripts (helper_lib.py, parallel.py, post_execution.py) and the
fake_exporter test suite migrated too.

paths.py: subproc_path() now returns testium_path() — both point at
the testium package directory since the subprocesses live inside.

pyproject.toml: removed exclude=["lua_func", "py_func"] (no longer
needed), added package-data for testium.lua_func/*.lua, removed the
license classifier (PEP 639 conflict with license expression).

Subprocess isolation contract: py_func/ and lua_func/ may only import
runtime/ and their own modules — never interpreter/, main_win/, api/,
or testium/. Enforced by test/validation/items/isolation/ which runs a
py_func that statically scans subprocess source files for forbidden
imports. The contract holds today; the test prevents future drift.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/pyproject.toml

@@ -13,7 +13,6 @@ license-files = ["../LICENSE"]
 classifiers = [
   "Development Status :: 5 - Production/Stable",
   "Programming Language :: Python",
-  "License :: OSI Approved :: European Union Public Licence 1.2 (EUPL 1.2)",
 ]
 dependencies = [
     "setuptools",
@@ -36,7 +35,9 @@ testium = "testium:main"
 
 [tool.setuptools.packages.find]
 where=["."]
-exclude=["lua_func", "py_func"]
+
+[tool.setuptools.package-data]
+"testium.lua_func" = ["*.lua"]
 
 [tool.setuptools.dynamic]
 version = {file = ["VERSION"]}