cover anyio’s NoEventLoopError without altering existing behavior

[gotsysdba]

Fixes #144

Note once the minimal version of anyio ≥ 4.11, the backward compatibility code can be removed:

---

# anyio.NoEventLoopError was added in anyio 4.11. anyio 4.10 is still supported
# (via the langgraph/evaluation extras), where the attribute does not exist.
# Once the minimum anyio version is ≥ 4.11, replace this with a plain
# tuple and catch anyio.NoEventLoopError directly (commented out below)
_NO_LOOP_ERRORS: tuple[type[BaseException], ...] = (AsyncLibraryNotFoundError,)
if hasattr(anyio, "NoEventLoopError"):
    _NO_LOOP_ERRORS = (*_NO_LOOP_ERRORS, anyio.NoEventLoopError)


def get_execution_context() -> AsyncContext:
    """
    Return one of:
    - 'sync'         → plain synchronous context (no loop, no worker thread)
    - 'sync_worker'  → synchronous worker thread (spawned by to_thread.run_sync)
    - 'async'        → running inside the event loop
    """
    try:
        anyio.get_current_task()
        return AsyncContext.ASYNC
    # except (AsyncLibraryNotFoundError, anyio.NoEventLoopError): # anyio>4.10
    except _NO_LOOP_ERRORS:

Replace with:

def get_execution_context() -> AsyncContext:
    """
    Return one of:
    - 'sync'         → plain synchronous context (no loop, no worker thread)
    - 'sync_worker'  → synchronous worker thread (spawned by to_thread.run_sync)
    - 'async'        → running inside the event loop
    """
    try:
        anyio.get_current_task()
        return AsyncContext.ASYNC
    except (AsyncLibraryNotFoundError, anyio.NoEventLoopError):