* feature: we can check if a fileId is already in the cache
We using this to protect cache from adding the same needle to
the cache over and over.
* fuse mount: Do not start dowloader if needle is already in the cache
* added maxFilePartSizeInCache property to ChunkCache
If file very large only first maxFilePartSizeInCache bytes
are going to be put to the cache (subject to the needle size
constrains).
* feature: for large files put in cache no more than prescribed number of bytes
Before this patch only the first needle of a large file was intended for
caching. This patch uses maximum prescribed amount of bytes to be put in
cache. This allows to bypass default 2MB maximum for a file part stored
in the cache.
* added dummy mock methods to satisfy interfaces of ChunkCache
The patch addresses #3745.
The cache should return the exact amount of data requested by the buffer.
By construction of the cache it is always all requested data range
or we have error happening.
The old use of minsize miscalculate the requested data size,
if non zero offset is requested.
