resolve some bugs in kalloc.c

See merge request T202410359994318/project2608132-273837!6

- /内核描述
- /内核描述.md

refresh README.md

See merge request T202410359994318/project2608132-273837!5

# Conflicts:
#   README.md

Define buffer cache system for disk I/O operations:
- Add buf struct with disk sector tracking and lock mechanism
- Implement core buffer operations (init, read, write, release)
- Set fixed BSIZE of 512 bytes per buffer

Buffer cache provides synchronized disk access and caching layer
between filesystem and disk device.

Added additional UART register definitions and error checking masks.
--spinlock.h
Added a declaration for printstring function.
--sdcard.h
No changes needed.
--proc.h
Added a priority field to the proc struct.
--printf.h
Added a declaration for printstring function.

- Add pipe_status_t enum for error handling
- Implement parameter validation
- Add proper cleanup in error cases
- Update return values to use status codes
- Add timeout support infrastructure
- Improve error propagation

dev: +2

Dev3

See merge request T202410359994318/project2608132-273837!4

修改了内存分配算法，使用伙伴系统进行分配，并添加了测试文件进行测试

See merge request T202410359994318/project2608132-273837!3

# Conflicts:
#   kernel/kalloc.c
#   xv6-user/test.c

Implement Priority-Based Scheduling in Scheduler

See merge request T202410359994318/project2608132-273837!2