Validate --cache-location and --log-location options early with actionable warnings

[Copilot]

Two silent failure modes: a typo in --cache-location (e.g. /.triton/cache vs ~/.triton/cache) caused instrumentation to run against a wrong/empty directory with no feedback; a missing parent directory for -l /path/to/output.json caused output to be silently dropped.

Changes

• is_triton_cache_dir(path) — new helper that returns True only if the directory contains at least one subdirectory (Triton's per-kernel hash dirs). Empty directories fail the check.

• --cache-location validation — when the path exists as a directory but passes no subdirectory check, emit:

  WARNING: Cache location /path exists but appears to be empty or not a Triton cache
  directory. Instrumented kernels may not be found there.
  

• --log-location parent-dir validation — when the parent directory is missing, attempt os.makedirs() (mirroring existing --cache-location behavior); fall back to console with a clear error on OSError. Also fixes the misleading "either doesn't exist or it is a directory" warning — that branch is only reachable when the path is a directory.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Option validation in Omniprobe</issue_title>
<issue_description>One area for improvement (and reduces support requests) is error handling w.r.t. command line arguments, e.g.

• User made a typo in the path to the Triton cache: /.triton/cache instead of ~/.triton/cache. Instrumentation was happening, but instrumented kernels were never found. We may want to check if the provided directory is indeed a Triton cache directory.
• When writing output to file with -l /path/to/output.json, if the path does not exist, no output is written. We should either create the directory (if permissions allow), or catch and report the error early.</issue_description>

Comments on the Issue (you are @copilot in this section)

@rwvo May have been addressed already, but I'll ask copilot to check, and implement if it hasn't been.

• Fixes Option validation in Omniprobe #24

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