Allow users to set jitify cache file limit via an environment variable

[trxcllnt]

Jitify limits the file count of the kernel cache, defaulting to the number of JIT kernels to keep in memory.

Limiting to 100 files on disk leads to thrashing if running workloads that exercise all the binops (like unit tests).

This PR adds a LIBCUDF_KERNEL_CACHE_FILE_LIMIT environment variable so users can control the number of files Jitify should keep on disk.

[codecov]

Codecov Report

Merging #8132 (f1d46ae) into branch-0.20 (51336df) will increase coverage by 0.03%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.20    #8132      +/-   ##
===============================================
+ Coverage        82.88%   82.92%   +0.03%     
===============================================
  Files              103      104       +1     
  Lines            17668    17896     +228     
===============================================
+ Hits             14645    14840     +195     
- Misses            3023     3056      +33     

Impacted Files	Coverage Δ
python/cudf/cudf/_fuzz_testing/parquet.py	0.00% <ø> (ø)
python/cudf/cudf/_fuzz_testing/utils.py	0.00% <ø> (ø)
python/cudf/cudf/core/abc.py	91.66% <ø> (+0.17%)	⬆️
python/cudf/cudf/core/algorithms.py	82.35% <ø> (ø)
python/cudf/cudf/core/column/__init__.py	100.00% <ø> (ø)
python/cudf/cudf/core/column/categorical.py	92.37% <ø> (+0.13%)	⬆️
python/cudf/cudf/core/column/column.py	88.20% <ø> (-0.44%)	⬇️
python/cudf/cudf/core/column/datetime.py	88.03% <ø> (-1.88%)	⬇️
python/cudf/cudf/core/column/decimal.py	91.04% <ø> (-1.89%)	⬇️
python/cudf/cudf/core/tools/datetimes.py	80.42% <0.00%> (-4.11%)	⬇️
... and 36 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 44f21b3...f1d46ae. Read the comment docs.

[cwharris]

so code much wow 🐕

[trxcllnt]

@gpucibot merge