add back some backtrader compat imports #27

Job	Run time
Build Windows arm64 wheels (windows-11-arm)	10m 43s
Build MacOS x86_64 wheels (macos-13)	9m 31s
Build MacOS arm64 wheels (macos-14)	4m 56s
Build Linux x86_64 wheels (ubuntu-22.04)	17m 8s
Build Windows x86 wheels (windows-2022)	7m 41s
Build Windows amd64 wheels (windows-2022)	7m 22s
Build Linux arm64 wheels (ubuntu-22.04-arm)	18m 25s
	1h 15m 46s

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