Use the zstdframe package where sensible instead of plumbing
around our own zstd.Encoder just for stateless operations.
This causes logtail to have a dependency on zstd,
but that's arguably okay since zstd support is implicit
to the protocol between a client and the logging service.
Also, virtually every caller to logger.NewLogger was
manually setting up a zstd.Encoder anyways,
meaning that zstd was functionally always a dependency.
Updates #cleanup
Updates tailscale/corp#18514
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
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