This moves the logic rendering NARs to a struct using the
previously introduced, more granular BlobService, ChunkService and
DirectoryService.
Instead of passing them around to the helper functions, they're kept as
members of a struct.
Remove the async invocations in the nar_renderer tests, there's nothing
async in here.
Change-Id: Ic6d24aaad68a1fda46ce29f2cdb5f7b87f481d5c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8095
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
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