perf python: Port stackcollapse to perf module

Port stackcollapse.py from tools/perf/scripts/python/ to a standalone
script in tools/perf/python/ refactored into a StackCollapseAnalyzer
class.

Improvements compared to the legacy script:
- Traverse sample.callchain directly from perf.session without
  allocating per-event dictionaries, and fall back to sample.symbol when
  a sample has no callchain.
- Replace deprecated optparse with argparse, adding -i/--input alongside
  --include-tid, --include-pid, --no-comm, --tidy-java, and --kernel.
- Handle BrokenPipeError cleanly when output is piped into downstream
  tools (such as head or flamegraph.pl).

Add a shell test (test_stackcollapse_python.sh) using a CPU workload
(perf test -w noploop) to verify the standalone script.

Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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