[Feature]: Add integration tests for Tracer profiling engine

[KaykCaputo]

Summary

Add integration tests that exercise the core tracing engine (Tracer._trace, get_trace_data, show_results) against real Python code, not just _is_user_code path filtering.

Problem

tests/test_tracer.py covers 12 scenarios for _is_user_code() (stdlib, site-packages, venv markers, symlinks, etc.) but does not verify that profiling actually records function calls, timings, callee relationships, or call-tree output. A regression in _trace() or get_trace_data() would go undetected.

Proposed Solution

Add a new test module (e.g. tests/test_tracer_integration.py) with small fixture scripts that:

1. Start/stop a Tracer around runpy.run_path() or an inline function call
2. Assert get_trace_data() returns expected function keys, call counts, and total times
3. Cover --ignore pattern filtering via _get_key() / _is_ignored()
4. Cover exception stack unwinding (the fallback path in _trace() when return frame doesn't match stack top)
5. Optionally test the public API (start_trace, stop_trace, show_results) exported from oracletrace/__init__.py

Use Case

The tracer is the core of OracleTrace. Integration tests give confidence that profiling, aggregation, and filtering work end-to-end — especially after changes to _trace() or user-code detection.

Example (optional)

# Fixture script: calls nested functions with known structure
def outer():
    inner()

def inner():
    pass

outer()

# Expected trace keys like "script.py:outer", "script.py:inner"
# Expected call_count and callee relationships

Alternatives Considered

• Extend tests/test_tracer.py in place — possible, but separation keeps unit vs integration tests clear.
• Only add CLI-level tests — CLI tests mock Tracer and would not catch engine regressions.

Additional Context

Currently untested in oracletrace/tracer.py:

• _trace() call/return handling and exception unwind (lines 174–215)
• get_trace_data() (lines 271–296)
• show_results() table and logic-flow tree (lines 217–269)
• Public helpers start_trace / stop_trace (lines 302–322)

Checklist

• I searched existing issues before opening this request
• I described the problem and why this feature is useful
• I provided enough detail for implementation discussion