fix: free stale embedding engines when switching provider classes #57

Job	Run time
linux-musl-arm64-remote build + test	1m 16s
linux-arm64-full build + test	2m 58s
linux-x86_64-local build + test	3m 9s
macos-local build + test	3m 22s
macos-x86_64-local build	2m 33s
linux-musl-x86_64-remote build + test	1m 20s
macos-arm64-local build + test	3m 8s
macos-x86_64-full build	2m 15s
linux-musl-x86_64-full build + test	4m 17s
windows-x86_64-remote build + test	7m 15s
linux-x86_64-remote build + test	1m 24s
macos-full build + test	4m 53s
macos-arm64-full build + test	3m 18s
macos-remote build + test	1m 56s
linux-arm64-local build + test	2m 50s
linux-arm64-remote build + test	1m 42s
linux-x86_64-full build + test	2m 41s
macos-x86_64-remote build	1m 20s
linux-musl-arm64-full build + test	3m 8s
linux-musl-x86_64-local build + test	3m 56s
windows-x86_64-local build + test	3m 55s
macos-arm64-remote build + test	2m 9s
linux-musl-arm64-local build + test	3m 12s
ios-remote build	1m 59s
android-x86_64-remote build + test	3m 5s
ios-sim-remote build	1m 50s
apple-xcframework build	16m 28s
android-arm64-v8a-remote build	58s
android-aar build	10m 59s
ios-local build	2m 11s
android-x86_64-full build + test	4m 40s
android-arm64-v8a-local build	2m 44s
ios-sim-full build	5m 52s
windows-x86_64-full build + test	9m 31s
android-armeabi-v7a-remote build	1m 16s
android-arm64-v8a-full build	3m 2s
ios-full build	3m 53s
android-x86_64-local build + test	4m 22s
ios-sim-local build	3m 26s
release	0s
	2h 24m 13s

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