Fix integral conversion and brace elision warnings

[Daniel Jump (DanielJump)]

These sites produce MSVC warnings under /Wall on both x64 and x86, which forces consumers building at high warning levels to wrap every C++/WinRT include in #pragma warning blocks.

Warning	Sites	Cause
C5246	most of base_identity.h	std::array aggregate init needs two brace levels
C4365	base_collections_base.h, base_collections_vector.h, base_string.h, base_error.h, base_types.h	integral promotion, and uint32_t -> ptrdiff_t iterator arithmetic on 32-bit
C4826	base_events.h	reinterpret_cast of a pointer to int64_t sign-extends
C4946	base_implements.h	reinterpret_cast between related classes; every abi type derives from unknown_abi, so static_cast is correct

Two are worth calling out:

to_hstring used std::copy to widen char to wchar_t. The assignment happens inside <xutility>, so a caller cannot silence it; std::transform with an explicit cast can. to_chars only writes ASCII there, so the cast is exact. Minimal repro:

// cl /std:c++20 /W4 /w14365
#include <algorithm>
#include <iterator>
char narrow[8]{};
wchar_t wide[8]{};
wchar_t* widen() { return std::copy(std::begin(narrow), std::end(narrow), wide); }

is_weak_ref took intptr_t and tested value < 0 while every caller holds a uintptr_t. It now takes uintptr_t and tests the high bit explicitly.

No generated files change, and no public signatures change.

Validated on a translation unit exercising implements<>, delegates, events, all collection flavours, coroutines, agile_ref, weak_ref, boxing and error handling.

Part of #1620.

[Copilot]

🟢 Approval recommended

The warning fixes are behavior-preserving, appropriately scoped, and covered by existing collection, string, event, weak-reference, and COM tests.

0 open findings

What changed in this PR

Eliminates MSVC /Wall warnings in foundational C++/WinRT headers without changing intended behavior or public APIs.

Changes:

• Adds explicit integral and iterator-offset conversions.
• Corrects std::array aggregate initialization.
• Introduces ABI-aware casting and explicit weak-reference/pointer bit handling.

File	Description
strings/​base_types.h	Makes narrowing conversions explicit.
strings/​base_string.h	Fixes reference-count, string-size, and character-widening warnings.
strings/​base_implements.h	Adds ABI casting and explicit weak-reference detection.
strings/​base_identity.h	Corrects array braces and integral conversions.
strings/​base_events.h	Converts encoded pointers without sign-extension warnings.
strings/​base_error.h	Explicitly converts HRESULT values for FormatMessageW.
strings/​base_collections_vector.h	Uses iterator-compatible offsets.
strings/​base_collections_base.h	Uses ptrdiff_t for iterator arithmetic.

🧠 Review effort: Balanced

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