fix(editor): expose filesystem info for checkpoints

[dsent]

What

• expose FS.getInfo(path, filtertype, vfs) through the runtime filesystem adapter
• define the returned FileInfo shape for LuaCATS-aware editor tooling
• mirror the same metadata API in the test backend using lfs.attributes
• route FS.exists through FS.getInfo
• cover metadata shape and type filtering in the filesystem specs

Why

The checkpoint timestamp lookup calls FS.getInfo, but the adapter only exposed FS.exists. The missing method crashes the first checkpoint attempt. This isolates the adapter fix as one commit on top of aldum/dev.

API compatibility

The production FS.exists signature was already (path, filtertype, vfs). This change adds the optional filtertype argument only to the test backend, bringing it in line with production. Omitting the argument still passes nil and checks for any filesystem entry, so existing one-argument calls keep the same behavior. Existing production callers use the filter to distinguish files from directories.

FileInfo.type is a love.FileType; size and modtime are optional because LÖVE may be unable to determine them. The test backend uses lfs.attributes, which follows symbolic links, so it maps only LuaFileSystem's file and directory modes directly and reports other modes as LÖVE's other. It does not claim symlink semantics.

Validation

• tests/util/fs_spec.lua: 9 successes, 0 failures, 0 errors
• full Lua 5.1 suite: 687 successes, 0 failures, 0 errors
• luac5.1 -p src/util/filesystem.lua tests/util/fs_spec.lua
• git diff --check origin/dev...HEAD

[dsent]

@aldum I must clarify that I encountered this bug using the branch with a heavily updated editor that we now use for lessons. Didn't realize this at the moment. Thus, the bug was caused by the code that we've just wrote and that is not yet merged.

However, I explored the options and came to a conclusion that this is, in fact, not a bad solution. We save checkpoints and need to check the last modification time. The only way to do that without adding any new API seemed to read the current project object and iterate over all files until a matching one is found. This is quite ugly imo (and I'm not sure it gets regenerated often).

link/symlink rename is removed as it defends against a situation that should not happen. Type annotations added.