fix: correct depth tracking in CallTracer only_top_call mode

[0xMuang]

Summary

• Fixed depth tracking bug in CallTracer when only_top_call is enabled
• Previously, nested calls would cause the root frame to be popped prematurely

Problem

When only_top_call was enabled:

1. push_frame skipped nested calls without incrementing depth
2. pop_frame checked depth > 1 which was false (depth stayed at 1)
3. This caused root frame to be popped when nested call ended

Fix

Now depth is incremented before the early return check, so pop_frame correctly skips nested call endings.

Test

• 3 line change in crates/execution/src/inspector/call_tracer.rs

Reported by @qj0r9j0vc2 in PR #115