Fix crash on component unload, catch panics at the FFI boundary, export SetPlatformCapabilities

[Linklsk]

The crash

The component brings 1C down when the platform unloads it. Reproduced on 1C 8.5.4.1306, both
x86 and x86_64.

destroy_component reads the destructor pointer through a local ComponentWrapper which assumes
destroy sits right after the four interface pointers. In Component five fields are declared in
between, so the real offset was 96 on x86_64 and 48 on x86, while the wrapper read 32 and 16. That
slot holds memory_manager_ptr, which set_mem_manager fills with a live pointer to the platform
allocator — so DestroyObject called it as a function.

Windows Error Reporting matches this exactly: 1CV8C.exe, event type BEX, c0000005, DEP flag 8,
and StackHash in P4, meaning the faulting address belongs to no loaded module.

Pinned by a test rather than by inspection — this assertion fails on main:

assertion `left == right` failed
  left: 96      // actual offset of `destroy`
 right: 32      // where ComponentWrapper reads it

The fix moves destroy to the offset the wrapper expects and adds offset_of! assertions plus a
create → destroy roundtrip test, both running on x86_64 and i686.

Panics

Every platform callback except set_mem_manager now runs behind a guard. A panic in add-in code used
to unwind through the C++ frames of 1C and abort the process; now it is caught, reported through
AddError, and turned into the failure value the platform expects. The component is poisoned after
the first panic, since its state is unknown once the stack has unwound.

init also stores connection_ptr before running add-in code. The field existed but was never
populated anywhere, so the FFI layer had no way to reach AddError. This is what makes a panic inside
init itself reportable.

SetPlatformCapabilities

Now exported by extern_functions!. Per the Native API documentation, without this export the platform
withholds message output — so Connection::add_error and the whole MessageCode enum were dead code.
The pre-existing PLATFORM_CAPABILITIES static loses its mut, since references to static mut
become errors in edition 2024.

tVariant conversion

From<&TVariant> for ParamValue handled only Int32 and Double, silently turning VTYPE_I2,
VTYPE_UI1, VTYPE_UI2, VTYPE_ERROR and VTYPE_R4 into ParamValue::Empty. The docs note that
values arriving from the web client may come with any numeric type.

Taken from your feat/support-for-any-func-args-and-return

• 96954c4 cherry-picked as is, with your authorship: os_string_nil did not append the terminator on
  unix while get_str reads names including it, so find_prop and find_method could never match on
  Linux. These fixes are independent of the Any feature, so they are split out here.
• The lifetime elision in This::get_component, the explicit lifetime on ParamValues::iter, and
  #[allow(dead_code)] on name_override. They clear three of the four pre-existing clippy warnings.

Verification

• cargo test --workspace — 84 passed, 0 failed
• cargo test -p native_api_1c_core --target i686-pc-windows-msvc — 15 passed, so the layout
  assertions run on 32-bit too
• cargo clippy --workspace --all-targets — one pre-existing warning left (string_utils.rs:42)
• cargo fmt --all -- --check — clean. Note that find_method.rs and find_prop.rs still make rustfmt
  abort with an internal left behind trailing whitespace error, which predates this branch
• Checked end to end in 1C 8.5.4.1306 on both x86 and x86_64: the component loads, properties and
  methods work, and a deliberate panic is reported into the message window instead of killing 1C

Left alone

• dtor is 0 in all four vtables. If the platform ever calls the virtual destructor instead of
  DestroyObject, that is a jump to null with the same signature as the bug fixed here.
• A consumer building with panic = "abort" disables the guard entirely — noted in the README.
• No embedded manifest, and the CRT is linked dynamically (VCRUNTIME140.dll), while the 1C docs ask
  for non-system runtimes to be linked statically and for a manifest in Windows components.