summary: add full-pipeline E2E tests for string_patterns

Add comprehensive end-to-end tests that exercise the complete path:
raw trace2 JSON events -> parse -> apply -> prepareDataset ->
ToTraces -> extract OTLP span attributes -> verify summary JSON.

These tests are designed to be adversarial and expose any gaps in
the data flow. They cover:

 - Process-level data events (nesting=1) promoted at dl:summary
 - Region-level data events (nesting=2) with a proper region stack:
   value appears in BOTH the summary and the region's own data
 - Orphaned nested data events (nesting=2 with no region stack):
   previously would have crashed due to the off-by-one bounds bug;
   now the value is promoted and region attachment fails silently
 - Multiple data events accumulating in the same field as an array
 - Non-matching events excluded (wrong category, wrong key prefix)
 - Integer values from data events (not just strings)
 - Coexistence with message_patterns and region_timers in one summary
 - Promoted values visible at ALL detail levels (summary/process/verbose)
 - No summary config at all (nil) doesn't crash
 - No string_patterns configured doesn't create spurious entries
 - Data events from non-main threads
 - Deeply nested events (nesting=5) with only a partial region stack
 - Multiple rules matching different categories independently

Also replaces the earlier single-event e2e test with a richer
version using the test harness infrastructure (x_make_* helpers,
load_test_dataset_with_config, extractSummaryJSON).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: derrickstolee