fix(iracing): fix non-Latin driver names showing as ??? in session YAML

[mvoof]

Problem

Driver names with Cyrillic (and other non-Latin) characters appeared as ?
in the session YAML. Two root causes:

1. session_yaml() always decoded bytes as CP-1252, but iRacing now sends
   the session string as UTF-8 when irsdkUTF8SessionStr is set (introduced
   to support international names). UTF-8 bytes decoded as CP-1252 → ?.

2. For the non-UTF-8 fallback path, CP-1252 was hardcoded. On Russian Windows
   the system ACP is CP-1251, so Cyrillic bytes were still corrupted even
   before iRacing added the UTF-8 flag.

Changes

• session_yaml() now reads the irsdkUTF8SessionStr telemetry variable at
  runtime and switches to String::from_utf8_lossy when it is non-zero.
• decode_cp1252 now calls GetACP() (Win32) to pick the correct codec from
  encoding_rs based on the actual system locale instead of always using
  CP-1252. Supports CP-1251/1250/1253/1254/1255/1256/1257/1258/874/932/936/949/950.
• Added Win32_Globalization feature to the windows-sys dependency.

[gemini-code-assist]

Code Review

This pull request adds support for UTF-8 session strings in iRacing telemetry and dynamically resolves the Windows system Active Code Page (ACP) instead of hardcoding CP-1252. Feedback suggests caching the resolved system ACP encoding using std::sync::OnceLock to avoid the overhead of calling the FFI function GetACP() on every string decoding operation.

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[gemini-code-assist]

Calling GetACP() on every string decoding operation can introduce unnecessary FFI overhead, especially since telemetry string decoding can happen multiple times per frame. Since the system active code page (ACP) does not change during the lifetime of the process, we can cache the resolved encoding using std::sync::OnceLock to completely eliminate this overhead after the first call.

fn system_acp_encoding() -> &'static encoding_rs::Encoding {
    static ENCODING: std::sync::OnceLock<&'static encoding_rs::Encoding> = std::sync::OnceLock::new();
    *ENCODING.get_or_init(|| {
        #[cfg(all(windows, any(feature = "iracing", feature = "ac-evo", feature = "lmu")))]
        {
            // SAFETY: GetACP() is always safe to call and never fails.
            let acp = unsafe { windows_sys::Win32::Globalization::GetACP() };
            match acp {
                1251 => encoding_rs::WINDOWS_1251,
                1252 => encoding_rs::WINDOWS_1252,
                1250 => encoding_rs::WINDOWS_1250,
                1253 => encoding_rs::WINDOWS_1253,
                1254 => encoding_rs::WINDOWS_1254,
                1255 => encoding_rs::WINDOWS_1255,
                1256 => encoding_rs::WINDOWS_1256,
                1257 => encoding_rs::WINDOWS_1257,
                1258 => encoding_rs::WINDOWS_1258,
                874  => encoding_rs::WINDOWS_874,
                932  => encoding_rs::SHIFT_JIS,
                936  => encoding_rs::GBK,
                949  => encoding_rs::EUC_KR,
                950  => encoding_rs::BIG5,
                _    => encoding_rs::WINDOWS_1252,
            }
        }
        #[cfg(not(all(windows, any(feature = "iracing", feature = "ac-evo", feature = "lmu"))))]
        {
            encoding_rs::WINDOWS_1252
        }
    })
}