Exposing GGMLLogLevel for custom log callbacks

[mmende]

The log level enum must have been changed at some point (e.g. GGML_LOG_LEVEL_DEBUG is now 1 instead of 4). The bindings are updated in this regard. I also made GGMLLogLevel public such that it can be used to implement custom logging logic, e.g.:

use log::{debug, error, info, trace, warn};
use whisper_rs::GGMLLogLevel;

pub unsafe extern "C" fn whisper_log_fn(
    level: u32,
    text: *const std::os::raw::c_char,
    _: *mut std::os::raw::c_void, // user_data
) {
    if text.is_null() {
        error!("whisper_log_fn: text is nullptr");
    }

    // SAFETY: we must trust whisper.cpp that it will not pass us a string that does not satisfy
    // from_ptr's requirements.
    let log_str = unsafe { std::ffi::CStr::from_ptr(text) }.to_string_lossy();
    // whisper.cpp gives newlines at the end of its log messages, so we trim them
    let trimmed = log_str.trim();

    let level = GGMLLogLevel::from(level);

    match level {
        GGMLLogLevel::None => debug!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Debug => debug!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Info => info!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Warn => warn!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Error => error!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Cont => trace!(target: "whisper", "{}", trimmed),
        GGMLLogLevel::Unknown(level) => warn!(
            target: "whisper",
            "whisper_log_fn: unknown log level {}: message: {}", level, trimmed
        ),
    }
}


fn main() {
    unsafe {
        whisper_rs::set_log_callback(Some(whisper_log_fn), std::ptr::null_mut());
    }
}