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>

test/robustness/console serial/terminal_bug_reproducer.py

@@ -1,4 +1,4 @@
-import libs.testium as tm
+import api.testium as tm
 
 def RetreiveData(console_name):
     print("--------------- retrieving data ---------------")

test/robustness/console terminal/terminal_bug_reproducer.py

@@ -1,4 +1,4 @@
-import libs.testium as tm
+import api.testium as tm
 
 def RetreiveData(console_name):
     print("--------------- retrieving data ---------------")

test/validation/items/common/helper_lib.py

@@ -1,4 +1,4 @@
-import libs.testium as libtm
+import api.testium as libtm
 
 
 def check_os(expected_os):

test/validation/items/isolation/check_isolation.py

@@ -0,0 +1,65 @@
+"""Static check that py_func/ and lua_func/ subprocess code does not depend
+on testium internals. The contract is:
+
+    py_func/*.py  may import:  py_func.*, runtime.*, plus stdlib/3rd-party
+    lua_func/*.lua may require: lua_func/<own files>, plus lua stdlib
+
+Forbidden top-level modules: interpreter, main_win, api, testium.
+"""
+
+import ast
+import os
+import re
+
+FORBIDDEN_PY = {"interpreter", "main_win", "api", "testium"}
+FORBIDDEN_LUA = {"interpreter", "main_win", "api", "testium"}
+
+
+def _collect_py_imports(path):
+    with open(path, "r", encoding="utf-8") as f:
+        tree = ast.parse(f.read(), filename=path)
+    out = set()
+    for node in ast.walk(tree):
+        if isinstance(node, ast.Import):
+            for n in node.names:
+                out.add(n.name.split(".")[0])
+        elif isinstance(node, ast.ImportFrom):
+            if node.level == 0 and node.module:
+                out.add(node.module.split(".")[0])
+    return out
+
+
+def _collect_lua_requires(path):
+    with open(path, "r", encoding="utf-8") as f:
+        text = f.read()
+    return {m.split(".")[0] for m in re.findall(r'require\s*\(?\s*["\']([^"\']+)["\']', text)}
+
+
+def check_isolation(testium_dir):
+    failures = []
+
+    py_dir = os.path.join(testium_dir, "py_func")
+    for root, _, files in os.walk(py_dir):
+        for f in files:
+            if not f.endswith(".py"):
+                continue
+            p = os.path.join(root, f)
+            leaks = _collect_py_imports(p) & FORBIDDEN_PY
+            if leaks:
+                failures.append(f"py_func/{os.path.relpath(p, py_dir)} leaks: {sorted(leaks)}")
+
+    lua_dir = os.path.join(testium_dir, "lua_func")
+    for root, _, files in os.walk(lua_dir):
+        for f in files:
+            if not f.endswith(".lua"):
+                continue
+            p = os.path.join(root, f)
+            leaks = _collect_lua_requires(p) & FORBIDDEN_LUA
+            if leaks:
+                failures.append(f"lua_func/{os.path.relpath(p, lua_dir)} leaks: {sorted(leaks)}")
+
+    if failures:
+        for line in failures:
+            print(f"  - {line}")
+        return False
+    return True

test/validation/items/isolation/param.yaml

@@ -0,0 +1 @@
+no_param: Null

test/validation/items/isolation/test.tum

@@ -0,0 +1,8 @@
+- py_func:
+    name: py_func/lua_func do not depend on testium internals
+    file: $(test_path)$(psep)check_isolation.py
+    func_name: check_isolation
+    key: $(test)_PASS
+    param:
+        - $(testium_path)
+    expected_result: True

test/validation/items/parallel/parallel.py

@@ -1,5 +1,5 @@
 import time
-import libs.testium as tm
+import api.testium as tm
 
 
 def sleep_func(duration):