feat(vfs): 重构文件系统标志体系，区分打开标志与访问模式

[xboHodx]

• 将 ModeType 重命名为 InodeMode，明确其为inode权限位
• 将 FileMode 重命名为 FileFlags，明确其为文件打开标志（O_RDONLY等）
• 新增 FileMode 结构体，对应Linux内核的 file.f_mode，表示内核专用访问模式（FMODE_READ/FMODE_WRITE/FMODE_LSEEK等）
• 新增 InodeFlags 结构体，支持 S_SYNC、S_APPEND、S_IMMUTABLE 等inode标志
• 修复管道 poll 函数中的标志判断逻辑

[Copilot]

Pull request overview

This PR performs a comprehensive refactoring of file-related type names in the VFS layer to better align with Linux kernel semantics:

• Renames FileMode to FileFlags (user-space open flags like O_RDONLY, O_WRONLY, O_RDWR)
• Introduces a new FileMode type representing kernel-internal f_mode flags (FMODE_READ, FMODE_WRITE, etc.)
• Renames ModeType to InodeMode (inode permission bits like 0o755)
• Fixes pipe poll permission checking logic to use proper helper methods instead of direct flag checks

Key Changes

• New FileMode::open_fmode() function converts FileFlags to internal FileMode representation
• Enhanced permission checking in File::readable() and File::writeable() methods
• Pipe poll now uses is_write_only() and is_read_only() helper methods for clearer access mode checks

Reviewed changes

Copilot reviewed 100 out of 100 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
kernel/src/filesystem/vfs/file.rs	Core refactoring: adds new FileMode type, renames FileMode to FileFlags, implements conversion logic and permission checks
kernel/src/ipc/pipe.rs	Renames mode field to file_flags, fixes poll permission check logic using new helper methods
kernel/src/filesystem/vfs/syscall/mod.rs	Renames ModeType to InodeMode throughout syscall interfaces
kernel/src/filesystem/vfs/mod.rs	Updates IndexNode trait methods to use FileFlags parameter, updates InodeMode conversions
All other files	Mechanical renames of FileMode→FileFlags and ModeType→InodeMode across device drivers, filesystems, and system components

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