fix: respect process umask when creating files

[devk0n]

Summary

Use standard pre-umask creation modes for new files and directories so Oil respects the process umask.

Previously Oil requested:

• files as 0644
• directories as 0755

Because a process umask can only remove permission bits, users with a group-writable umask such as 0002 still received 0644 files and 0755 directories.

This changes the creation modes to:

• files: 0666
• directories: 0777

and allows the operating system to apply the process umask normally.

Example

With:

umask 0002

Oil now creates:

• files as 0664
• directories as 0775

With:

umask 0022

the existing behavior is preserved:

• files as 0644
• directories as 0755

With:

umask 0000

Oil creates:

• files as 0666
• directories as 0777

Implementation

Updated the creation modes used by:

• fs.touch
• mkdirp
• local directory creation
• macOS trash user-entry directory creation

Intentional private modes, such as secure temporary files and trash infrastructure using 0700, are left unchanged.

No post-creation chmod is performed.

Tests

Added integration coverage for both 0002 and 0022 umasks.

Verified with:

./run_tests.sh tests/files_spec.lua
./run_tests.sh
stylua --check lua tests
luacheck lua tests --formatter plain
./scripts/nvim-typecheck-action/typecheck.sh --workdir scripts/nvim-typecheck-action lua

All tests pass.