serde: add deserializer and remove useless code

[cosven]

http post http://127.0.0.1:23332/rpc/v1 jsonrpc='2.0' method='app.playlist.play_model' params:='[{"__type__": "feeluown.library.BriefSongModel","album_name": "吻别","artists_name": "张学友","duration_ms": "00:00","identifier": "bZn1Pb2Ei64","provider": "ytmusic","uri": "fuo://ytmusic/songs/bZn1Pb2Ei64","title": "吻别"}]' id=1

[coveralls]

Pull Request Test Coverage Report for Build 10545996589

Details

• 169 of 220 (76.82%) changed or added relevant lines in 7 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.3%) to 55.366%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
feeluown/serializers/init.py	21	23	91.3%
feeluown/serializers/plain.py	39	41	95.12%
feeluown/serializers/python.py	33	38	86.84%
feeluown/serializers/base.py	7	15	46.67%
feeluown/webserver/jsonrpc_.py	0	16	0.0%
feeluown/serializers/objs.py	47	65	72.31%

Files with Coverage Reduction	New Missed Lines	%
feeluown/webserver/jsonrpc_.py	1	0.0%
feeluown/serializers/python.py	1	91.43%

Totals
Change from base Build 10441767621:	0.3%
Covered Lines:	9973
Relevant Lines:	18013

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💛 - Coveralls