lace-platform: Implement filesystem support, BIOS, UEFI, ext4

[kukrimate]

Add a layered storage stack with portable partition mappers and filesystem drivers shared across platforms.

The BlockDevice trait provides sector-level I/O with default byte-level methods. BIOS implements this via INT 13h with internal bounce buffering; UEFI overrides the byte-level methods to use firmware DiskIO directly.

Portable GPT and MBR partition table parsers (using zerocopy) operate on any BlockDevice. The probe layer discovers platform block devices, probes partitions, and mounts ext4 filesystems. UEFI SimpleFileSystem (FAT) is registered directly from firmware.

FsError carries platform-specific I/O errors: DiskError on BIOS, uefi Status on EFI. An Invalid variant covers parse/format errors in shared code. Boot-disk-only discovery is supported on both platforms for fast boot paths.

[Copilot]

Pull request overview

Adds a cross-platform storage/filesystem layer to lace-platform, enabling block-device discovery and filesystem mounting across BIOS, UEFI, and mock targets, with portable GPT/MBR parsing and ext4 support.

Changes:

• Introduce lace-platform::fs module with BlockDevice/Filesystem abstractions and a shared probe layer.
• Add portable GPT/MBR partition parsers and an ext4 filesystem implementation (feature-gated).
• Implement platform-specific storage discovery for BIOS (INT 13h), UEFI (SimpleFileSystem + DiskIO), and mock.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 21 comments.

Show a summary per file

File	Description
lace-platform/src/mock/mod.rs	Exposes mock fs module.
lace-platform/src/mock/fs.rs	Mock storage discovery stubs returning empty results.
lace-platform/src/lib.rs	Exposes unified fs module at top level.
lace-platform/src/fs/mod.rs	Defines fs module layout and re-exports probe API/types.
lace-platform/src/fs/base.rs	Adds BlockDevice + filesystem trait model and FsError.
lace-platform/src/fs/probe.rs	Implements partition probing and filesystem mounting orchestration.
lace-platform/src/fs/gpt.rs	Adds portable GPT parsing.
lace-platform/src/fs/mbr.rs	Adds portable MBR/EBR parsing.
lace-platform/src/fs/ext4.rs	Adds ext4 implementation backed by ext4-view.
lace-platform/src/efi/mod.rs	Wires in UEFI fs module and re-exports fs traits/types.
lace-platform/src/efi/fs.rs	Implements UEFI FAT access + DiskIO-backed block device discovery.
lace-platform/src/bios/mod.rs	Wires in BIOS fs module and extends BIOS error type for disk errors.
lace-platform/src/bios/fs.rs	Implements BIOS INT 13h disk I/O + discovery + block device adapter.
lace-platform/Cargo.toml	Adds zerocopy and optional ext4-view; adjusts feature set.
Cargo.toml	Adds workspace dependency on ext4-view.
Cargo.lock	Records new dependency resolution (e.g., ext4-view, crc).

[Copilot]

Pull request overview

Copilot reviewed 16 out of 17 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 17 out of 18 changed files in this pull request and generated 5 comments.

[julian-klode]

This has gone through several iterations and design reviews in meetings; I am quite happy with the outcome so far.

We need to evaluate in a future step whether the boot logic should scan the current disk only and scan others only on explicit request, and we may want further changes for that.