samples: inline windows_main.rs into main.rs

[Copilot]

• Refactor 42 sample crates: inline windows_main.rs body into main.rs wrapped in #[cfg(windows)] mod imp, delete windows_main.rs
• Preserve crate-level inner attributes (e.g. core_app's #![cfg_attr(windows, windows_subsystem = "windows")])
• Promote mod bindings; (in services/time and windows/webview) to crate root with #[cfg(windows)] so files resolve correctly
• Clippy fixes for nightly: windows-core::imp::encode_pointer (not_unsafe_ptr_arg_deref) and HRESULT::message non-windows branch (needless_return)
• Further simplification: collapse mod imp { use …; pub fn main(){…} } + fn main(){imp::main()} directly into #[cfg(windows)] fn main(){ use …; … }. Items declared inside mod imp (helper fns, #[implement] structs, impls) now live as nested items inside fn main and inherit its use statements.
  • fn main is not pub.
  • Return type chosen per-sample ((), windows::core::Result<()>, std::io::Result<()>) — fully qualified in the signature so it's resolvable without needing top-level use.
  • services/time and windows/webview: use super::bindings::* → use crate::bindings::* (the inline fn main is at crate root, not inside a module).
  • direct3d12 keeps the mod imp shape: it contains a nested mod d3d12_hello_triangle { use super::*; } whose super cannot reach into a fn.
  • Removed two now-unused imports (core::* in device_watcher, core::Result in thread_pool_work).
• cargo check --workspace (Linux) passes
• cargo check --workspace --target x86_64-pc-windows-gnu passes (with --exclude test_no_std, which has an unrelated pre-existing duplicate-lang-item issue)
• cargo fmt --all applied