feat: add headless libretro core probe

core_probe.py loads a libretro core with no window, runs it for a
number of frames and reports the files it opened (strace), its log
lines, frame, audio and save-state hashes and its speed. bench repeats
a run after warm-up and gives median, mean, deviation and range; check
swaps one system file between runs and compares one observable.

--record writes a JSON record with the core build, frontend commit,
host and every input by hash, validated against
core-probe-record.schema.json. A busy host is refused, and a
repetition that disagrees with the first is flagged.

wiki/testing-guide.md

@@ -56,6 +56,7 @@ Every module in `tests/`, by the area it guards.
 | Hardware targets and systems | synthetic + target files | `test_extract_targets`, `test_lakka_targets`, `test_libretro_slugs`, `test_system_ids`, `test_system_selection`, `test_target_names`, `test_target_scrapers`, `test_target_systems`, `test_target_verify` |
 | Installer and downloads | loopback server | `test_check_release`, `test_download`, `test_install`, `test_install_cores`, `test_install_experience`, `test_install_app`, `test_install_from`, `test_install_offline`, `test_install_selection`, `test_install_tui` |
 | Handheld launchers | a pty as the console, fake installer and firmware tools, stubbed PortMaster dialogs | `test_handheld_launchers`, `test_port` |
+| Running cores | parsers on fixed inputs, a libretro core built from C in the test when a compiler exists | `test_core_probe` |
 | Truth and native export | synthetic + cached originals | `test_export_counts`, `test_export_native_layer`, `test_export_report`, `test_exporters`, `test_truth_data_dir_readers`, `test_truth_diff`, `test_truth_layout` |
 | Scrapers, upstream and provenance | inline sources, synthetic | `test_batocera_md5_list`, `test_check_freshness`, `test_contributing_text`, `test_coverage_cache`, `test_data_dir_refs`, `test_dataclass_defaults`, `test_dedup`, `test_doc_pages`, `test_doc_surfaces`, `test_elec_scrapers`, `test_fbneo_parser`, `test_find_pinned_revision`, `test_hash_merge`, `test_launchers`, `test_launchers_emudeck`, `test_launchers_recalbox`, `test_launchers_retrobat`, `test_launchers_retrodeck`, `test_launchers_retropie`, `test_launchers_rocknix`, `test_mame_devices`, `test_mame_parser`, `test_mame_ref_audit`, `test_optional_dependencies`, `test_profile_sync`, `test_prose_style`, `test_provenance`, `test_refresh_data_dirs`, `test_refresh_failures`, `test_refresh_stale`, `test_retrodeck_scraper_errors`, `test_romset_recipes`, `test_schema_semantic_gate`, `test_scraper_contract`, `test_site_availability`, `test_site_content_data`, `test_site_copy`, `test_site_cores`, `test_site_emulator_page`, `test_site_exports`, `test_site_funnel`, `test_site_images`, `test_site_picker`, `test_site_platform_hashes`, `test_site_r2_components`, `test_site_r2_css`, `test_site_r2_emulators`, `test_site_r2_entry`, `test_site_r2_gate`, `test_site_r2_nav`, `test_site_r2_p0`, `test_site_r2_reference`, `test_site_r2_systems`, `test_site_r2_wiki`, `test_site_r3_collection`, `test_site_r3_components`, `test_site_r3_css`, `test_site_r3_emulators`, `test_site_r3_entry`, `test_site_r3_nav`, `test_site_r3_p0`, `test_site_r3_reference`, `test_site_r3_systems`, `test_site_r3_wiki`, `test_site_r4_components`, `test_site_r4_css`, `test_site_r4_emulators`, `test_site_r4_entry`, `test_site_r4_merge`, `test_site_r4_p0`, `test_site_r4_reference`, `test_site_r4_search`, `test_site_r4_systems`, `test_site_r4_wiki`, `test_site_r5_components`, `test_site_r5_css`, `test_site_r5_emulators`, `test_site_r5_entry`, `test_site_r5_reference`, `test_site_r5_systems`, `test_site_r5_wiki`, `test_site_render`, `test_site_system_links`, `test_site_validation`, `test_site_weight`, `test_site_write`, `test_source_ref_targets`, `test_upstream`, `test_upstream_index`, `test_validate_pr`, `test_validate_pr_flow`, `test_validate_pr_hashes`, `test_workflow_paths` |