fix: improve applist loading by using JSON decoder from file stream

[HynoR]

What this PR does / why we need it?

直接读取文件时,会把文件内容拷贝到 content ，此时会有 2m 内存 (应用商店信息的json文件大小)，然后内存中的 content再被反序列化内容。
可以直接用 decoder 一步读文件并反序列化，省掉这个拷贝操作。节约 2m 内存

Summary of your change

更换流 decoder 方法，直接让 decoder 读文件解析出内容。节约流程中在堆上占用 2m 的内存, 解析流程不变。

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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