Add Equal Loudness Filter (#7019)

* Add Equal Loudness Filter

Signed-off-by: Martmists <martmists@gmail.com>

* NoneType return on __init__

Signed-off-by: Martmists <martmists@gmail.com>

* Add data to JSON as requested by @CenTdemeern1 in a not very polite manner

Signed-off-by: Martmists <martmists@gmail.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* 'modernize'

Signed-off-by: Martmists <martmists@gmail.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update audio_filters/equal_loudness_filter.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update equal_loudness_filter.py

* Update equal_loudness_filter.py

* Finally!!

* Arrgghh

Signed-off-by: Martmists <martmists@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>