feat(klog): Implement kernel log level management and procfs interface

[fslongjin]

• Introduced a new module for managing kernel log levels, mimicking Linux behavior.
• Added support for dynamic log level configuration via command line and procfs interface.
• Created a new /proc/sys/kernel/printk file for reading and writing log level settings.
• Updated existing logging mechanisms to utilize the new log level management system.
• Enhanced the QEMU startup script to allow setting log levels through environment variables.

This implementation improves logging flexibility and aligns with expected Linux functionality.

---

Note

Introduce Linux-like kernel loglevel control (cmdline + /proc/sys/kernel/printk), integrate filtering into logger/kmsg, and add QEMU env-based loglevel.

• Logging / klog:
  • Add debug/klog/loglevel with global KERNEL_LOG_LEVEL, LogLevel, and filtering (should_print, cmdline handler handle_loglevel_param).
  • Update libs/printk logger to filter by KERNEL_LOG_LEVEL, map log::Level to LogLevel, and push structured LogMessage to kmsg.
• Procfs:
  • Introduce /proc/sys/kernel/printk with read/write via sys::sysctl::PrintkSysctl (returns four loglevel fields; writes set console level).
  • Add procfs/sys tree creation; wire read/write paths in IndexNode::read_at/write_at for ProcSysKernelPrintk.
  • Refactor klog.rs to define LogMessage using shared LogLevel; update kmsg to use it and clone on push.
• Init / Cmdline:
  • Expose KernelCmdlineKV/EarlyKV fields and invoke handle_loglevel_param() during cmdline init.
• Tools:
  • Enhance tools/run-qemu.sh to accept DRAGONOS_LOGLEVEL env var and pass loglevel=N to kernel cmdline.

^{Written by Cursor Bugbot for commit 62909c0. This will update automatically on new commits. Configure here.}

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