Add immutabledict C code

Start trying to convert fundamental objects to
C as we now rely on a fairly small core of things,
and 1.4 is having problems with complexity added being
slower than the performance gains we are trying to build in.

immutabledict here does seem to bench as twice as fast as the
Python one, see below.  However, it does not appear to be
used prominently enough to make any dent in the performance
tests.

at the very least it may provide us some more lift-and-copy
code for more C extensions.

import timeit

from sqlalchemy.util._collections import not_immutabledict, immutabledict

def run(dict_cls):
    for i in range(1000000):
        d1 = dict_cls({"x": 5, "y": 4})

        d2 = d1.union({"x": 17, "new key": "some other value"}, None)

        assert list(d2) == ["x", "y", "new key"]

print(
    timeit.timeit(
        "run(d)", "from __main__ import run, not_immutabledict as d", number=1
    )
)
print(
    timeit.timeit(
        "run(d)", "from __main__ import run, immutabledict as d", number=1
    )
)

output:

python: 1.8799766399897635
C code: 0.8880784640205093

Change-Id: I29e7104dc21dcc7cdf895bf274003af2e219bf6d

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg2.py b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
index 1eaf63ff3..9585dd467 100644
--- a/lib/sqlalchemy/dialects/postgresql/psycopg2.py
+++ b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
@@ -658,7 +658,7 @@ class PGDialect_psycopg2(PGDialect):
     _has_native_jsonb = False
 
     engine_config_types = PGDialect.engine_config_types.union(
-        [("use_native_unicode", util.asbool)]
+        {"use_native_unicode": util.asbool}
     )
 
     colspecs = util.update_copy(