in I4e0b627bfa187f1780dc68ec81b94db1c78f846a the 1.4 version has more
changes than the main version, which failed to get the entire change,
yet the whole thing was merged.   Restore the missing mutex related
code to the main version.

Fixed regression where the fix for :ticket:`8098`, which was released in
the 1.4 series and provided a layer of concurrency-safe checks for the
lambda SQL API, included additional fixes in the patch that failed to be
applied to the main branch. These additional fixes have been applied.

Change-Id: Id172e09c421dafa6ef1d40b383aa4371de343864
References: #8098
Fixes: #9461

Fixed typing issue where :meth:`.ColumnElement.cast` did not allow a
:class:`.TypeEngine` argument independent of the type of the
:class:`.ColumnElement` itself, which is the purpose of
:meth:`.ColumnElement.cast`.

Fixes: #9451
Change-Id: I68119c6a9e8bf896715eea79be2b4f36b1c141de

Fixed regression where the :func:`_sql.select` construct would not be able
to render if it were given no columns and then used in the context of an
EXISTS, raising an internal exception instead. While an empty "SELECT" is
not typically valid SQL, in the context of EXISTS databases such as
PostgreSQL allow it, and in any case the condition now no longer raises
an internal exception.

For this case, also add an extra whitespace trim step for the unusual
case that there are no columns to render.  This is done in such a
way as to not interfere with other test cases that are involving
custom compilation schemes.

Fixes: #9440
Change-Id: If65ba9ce15d371f09b4342ad0669143b7b082a78

Added missing init overload to :class:`_sql.Numeric` to allow
type checkers to properly resolve the type var given the
``asdecimal`` parameter.

this fortunately fixes a glitch in the generate_sql_functions script
also

Fixes: #9391
Change-Id: I9cecc40c52711489e9dbe663f110c3b81c7285e4

Fixed typing bug where :meth:`_sql.Select.from_statement` would not accept
:func:`_sql.text` or :class:`.TextualSelect` objects as a valid type.
Additionally repaired the :class:`.TextClause.columns` method to have a
return type, which was missing.

Fixes: #9398
Change-Id: I627fc33bf83365e1c7f7c6ed29ea387dfd4a57d8

Validate that when provided the :paramref:`_sql.MetaData.schema`
argument of :class:`_sql.MetaData` is a string.

Change-Id: I4237232d2ee0f5a4d0b9dbd9af5f5b57abf395b4

Previously only the snake case versions nulls_last/nulls_first
were exported in the toplevel namespace.

Fixes: #9390
Change-Id: I9088e858ae108a5c9106b9d8d82655ad605417cc