Unify sync and async clients

[tinvaan]

The current implementation of Supabase's sync and async client contains a ton of redundant code that is shared between both classes and should ideally reside under one class.

This PR is an attempt to unify the two client classes and host them in one single SupabaseClient class. A single client class should in theory be easier to maintain and an significantly bumps the project's code coverage(up to 63% from 44% earlier).

py39 run-test: commands[1] | poetry run pytest -s --disable-warnings --cov=./ --cov-report=term --cov-report=html
Test session starts (platform: darwin, Python 3.9.18, pytest 8.0.1, pytest-sugar 1.0.0)
cachedir: .tox/py39/.pytest_cache
rootdir: /Users/harish/Workspaces/oss/supabase/supabase-py
plugins: sugar-1.0.0, cov-4.1.0, anyio-4.2.0
collected 52 items

 tests/test_client.py xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx                                                                                             94% █████████▌
 tests/test_client_options.py ✓✓                                                                                                                                    98% █████████▊
 tests/test_function_configuration.py ✓                                                                                                                            100% ██████████

---------- coverage: platform darwin, python 3.9.18-final-0 ----------
Name                              Stmts   Miss  Cover
-----------------------------------------------------
scripts.py                           11     11     0%
supabase/__init__.py                  7      0   100%
supabase/__version__.py               1      0   100%
supabase/client/__init__.py          10      0   100%
supabase/client/auth.py              10      2    80%
supabase/client/default.py          106     45    58%
supabase/client/exceptions.py         4      2    50%
supabase/lib/__init__.py              3      0   100%
supabase/lib/client_options.py       33      0   100%
supabase/lib/realtime_client.py      29     20    31%
-----------------------------------------------------
TOTAL                               214     80    63%
Coverage HTML written to dir htmlcov


Results (0.21s):
       3 passed
      49 xfailed
____________________________________________________________________________________ summary _____________________________________________________________________________________
  py39: commands succeeded
  congratulations :)

[tinvaan]

Test coverage is now up to 78% after the test suite revamp.

---------- coverage: platform darwin, python 3.9.18-final-0 ----------
Name                              Stmts   Miss  Cover
-----------------------------------------------------
scripts.py                           11     11     0%
supabase/__init__.py                  9      0   100%
supabase/__version__.py               1      0   100%
supabase/client/__init__.py          17      0   100%
supabase/client/default.py          133     24    82%
supabase/client/exceptions.py         4      0   100%
supabase/client/services.py          32      6    81%
supabase/lib/__init__.py              3      0   100%
supabase/lib/client_options.py       33      0   100%
supabase/lib/realtime_client.py      29     20    31%
-----------------------------------------------------
TOTAL                               272     61    78%
Coverage HTML written to dir htmlcov


Results (31.69s):
      17 passed
       1 skipped
  py39: OK (38.44=setup[3.35]+cmd[1.98,33.11] seconds)
  congratulations :) (38.50 seconds)