Memory leak on creating savepoints

I found a small memory leak when using many savepoints to the same DB.

Consider this code example:

session = create_session()

for _ in range(0, 5000):
    session.begin_nested()
    session.execute(
        sa.insert(Test).values(name='test'))
    session.commit()

session.commit()
session.close()

After this we can observe 5000 strings with savepoints names in memory.

Diging deeply into it I found that function sql/compiler.py:format_savepoint saves savepoint name to self._strings. By default savepoint names are unique for each nested transaction so saving them for future use is redundant and each new savepoint name stays in memory.

My proposition is to change the function, so savepoint name won't be saved:

    def format_savepoint(self, savepoint, name=None):
        value = name or savepoint.ident
        if self._requires_quotes(value):
            return self.quote_identifier(value)
        return value

Complete code example for reproducing bug in attachment.

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