interop: secsgem-py cross-validation harness + lenient identifier parsing

Adds a Docker-based interop harness that drives the C++ server with
secsgem-py 0.3.0 as the active host and probes a secsgem-py-passive
equipment from a minimal C++ active client.  Surfaces and fixes four
interoperability bugs uncovered by cross-testing:

  * SEMI E5 identifier formatcodes are a U1|U2|U4|U8 wildcard;
    secsgem-py picks the narrowest fitting width while our parsers
    only accepted U4.  `as_uN_scalar` / `as_iN_scalar` now accept
    any unsigned/signed width and range-check the downcast.
  * PPBODY (S7F3/F6) is "ASCII | Binary | List" per the spec;
    secsgem-py defaults to ASCII.  Added BINARY_OR_ASCII codegen
    item type with `as_text_or_binary` accessor.
  * S1F23/F24 Collection Event Namelist was unimplemented; added
    schema + `vids_for(ceid)` accessor on EventReportSubscriptions
    plus the dispatch handler.
  * S10F1 was registered as a host->equipment handler, but per
    SEMI E5 §12 S10F1 is equipment->host; S10F3 is the actual
    host->equipment Terminal Display Single.  Added an S10F3
    handler alongside (we keep S10F1 too for backward compat).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CMakeLists.txt

@@ -80,6 +80,9 @@ target_link_libraries(secs_server PRIVATE secsgem)
 add_executable(secs_client apps/secs_client.cpp)
 target_link_libraries(secs_client PRIVATE secsgem)
 
+add_executable(secs_interop_probe apps/secs_interop_probe.cpp)
+target_link_libraries(secs_interop_probe PRIVATE secsgem)
+
 # --- Tests ----------------------------------------------------------------
 enable_testing()
 include(FetchContent)