block: qcow: support compressed clusters (zlib, zstd)

Add support of reading and writing compressed clusters.
Support zlib and zstd compressions.

L2 cache: store entire L2 entries, not only standard cluster addresses.

Read path. Offsets of compressed clusters cannot be determined,
therefore replace QcowFile.file_offset_read() with QcowFile.file_read().
This method reads the cluster, decompresses it if necessary and returns
the data to the caller.

Write path. QcowFile.file_offset_write(): since writing to compressed
clusters is not generally possible, allocate a new standard
(non-compressed) cluster if compressed L2 entry is encountered; then
decompress compressed cluster into new cluster; then return offset
inside new cluster to the caller. Processing of standard clusters is
not changed.

Signed-off-by: Eugene Korenevsky <ekorenevsky@aliyun.com>

block/Cargo.toml

@@ -11,6 +11,7 @@ io_uring = ["dep:io-uring"]
 [dependencies]
 byteorder = { workspace = true }
 crc-any = "2.5.0"
+flate2 = "1.0"
 io-uring = { version = "0.7.10", optional = true }
 libc = { workspace = true }
 log = { workspace = true }
@@ -28,6 +29,7 @@ vm-memory = { workspace = true, features = [
 ] }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = { workspace = true }
+zstd = "0.13"
 
 [lints]
 workspace = true