perf(s3stream): prewarm MetaStream before stream ready to open

[lifepuzzlefun]

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[lifepuzzlefun]

awaitStreamReadyForOpen often cost 500ms+, but we can trigger prewarm the first need 64KB for metastream to reduce the read time.

[superhx]

awaitStreamReadyForOpen often cost 500ms+, but we can trigger prewarm the first need 64KB for metastream to reduce the read time.

@lifepuzzlefun The 500ms+ usually is the time cost of uploading WAL data to S3. Even if we pre-warm MetaStream, I think the MetaStream still needs to load more data from S3.

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