fix race conditions in lambda statements

fix race conditions in lambda statements

Fixed multiple observed race conditions related to :func:`.lambda_stmt`,
including an initial "dogpile" issue when a new Python code object is
initially analyzed among multiple simultaneous threads which created both a
performance issue as well as some internal corruption of state.
Additionally repaired observed race condition which could occur when
"cloning" an expression construct that is also in the process of being
compiled or otherwise accessed in a different thread due to memoized
attributes altering the ``__dict__`` while iterated, for Python versions
prior to 3.10; in particular the lambda SQL construct is sensitive to this
as it holds onto a single statement object persistently. The iteration has
been refined to use ``dict.copy()`` with or without an additional iteration
instead.

Fixes: #8098
Change-Id: I4e0b627bfa187f1780dc68ec81b94db1c78f846a