fix(xet): implement get_file_chunk_hashes after xet-core trait bump

[XciD]

xet-core main added a new get_file_chunk_hashes method on the Client trait. The release CI re-resolves branch = main (not --locked), so it picked up the new trait revision and our CachedXetClient failed E0046, blocking the v0.6.4 binary build (see failed run 26251717702).

This PR:

• Implements get_file_chunk_hashes on CachedXetClient by forwarding to self.inner (cache layer only handles reconstruction queries, not chunk hashes).
• Implements the same on the test-only MockClient shim.
• Bumps Cargo.lock to the latest xet-core main so local builds match CI.

Once merged, the v0.6.4 release workflow can be re-run and binaries will publish, unblocking the SkyPilot PR (skypilot-org/skypilot#9418) which needs v0.6.4 for the clone_fd fix.

[github-actions]

POSIX Compliance (pjdfstest)

============================================================
  pjdfstest POSIX Compliance Results
------------------------------------------------------------
  Files: 130/130 passed    Tests: 832 total (0 subtests failed)
  Result: PASS
------------------------------------------------------------
  Category               Passed    Total   Status
  -------------------- -------- -------- --------
  chflags                     5        5       OK
  chmod                       8        8       OK
  chown                       6        6       OK
  ftruncate                  13       13       OK
  granular                    5        5       OK
  mkdir                       9        9       OK
  open                       19       19       OK
  posix_fallocate             1        1       OK
  rename                     10       10       OK
  rmdir                      11       11       OK
  symlink                    10       10       OK
  truncate                   13       13       OK
  unlink                     11       11       OK
  utimensat                   9        9       OK
============================================================

[github-actions]

Benchmark Results

============================================================
  Benchmark — 50MB
------------------------------------------------------------
  Metric                                 FUSE          NFS
  ------------------------------ ------------ ------------
  Sequential read                    148.3 MB/s     209.2 MB/s
  Sequential re-read                2070.1 MB/s    2202.5 MB/s
  Range read (1MB@25MB)                0.5 ms         0.2 ms
  Random reads (100x4KB avg)           0.0 ms         0.0 ms
  Sequential write (FUSE)           1376.0 MB/s
  Close latency (CAS+Hub)            0.128 s
  Write end-to-end                   304.9 MB/s
  Dedup write                       1608.3 MB/s
  Dedup close latency                0.107 s
  Dedup end-to-end                   362.9 MB/s
============================================================
============================================================
  Benchmark — 200MB
------------------------------------------------------------
  Metric                                 FUSE          NFS
  ------------------------------ ------------ ------------
  Sequential read                    756.2 MB/s     643.5 MB/s
  Sequential re-read                2207.6 MB/s    2400.0 MB/s
  Range read (1MB@25MB)                0.2 ms         0.2 ms
  Random reads (100x4KB avg)           0.0 ms         0.0 ms
  Sequential write (FUSE)           1541.7 MB/s
  Close latency (CAS+Hub)            0.135 s
  Write end-to-end                   756.0 MB/s
  Dedup write                       1622.3 MB/s
  Dedup close latency                0.161 s
  Dedup end-to-end                   702.7 MB/s
============================================================
============================================================
  Benchmark — 500MB
------------------------------------------------------------
  Metric                                 FUSE          NFS
  ------------------------------ ------------ ------------
  Sequential read                   1275.8 MB/s     715.3 MB/s
  Sequential re-read                2076.7 MB/s    2391.9 MB/s
  Range read (1MB@25MB)                0.3 ms         0.2 ms
  Random reads (100x4KB avg)           0.0 ms         0.0 ms
  Sequential write (FUSE)           1456.0 MB/s
  Close latency (CAS+Hub)            0.117 s
  Write end-to-end                  1085.7 MB/s
  Dedup write                       1402.7 MB/s
  Dedup close latency                0.152 s
  Dedup end-to-end                   983.4 MB/s
============================================================
============================================================
  fio Benchmark Results
------------------------------------------------------------
  Job                        FUSE MB/s   NFS MB/s  FUSE IOPS   NFS IOPS
  ------------------------- ---------- ---------- ---------- ----------
  seq-read-100M                  318.5      456.6                      
  seq-reread-100M               2439.0       97.5                      
  rand-read-4k-100M                0.1        0.1         15         20
  seq-read-5x10M                 806.5      769.2                      
  rand-read-10x1M                  0.1        0.1         33         35
  Random Read Latency           FUSE avg      NFS avg
  ------------------------- ------------ ------------
  rand-read-4k-100M           68444.3 us   51079.8 us
  rand-read-10x1M             30275.5 us   28688.3 us
============================================================