Placeholder NAND archives can't be copied from fully read-only sources

[neobrain]

NixOS apparently defaults to installing to read-only locations even for owners. This breaks std::filesystem::copy in main.cpp.

I'm not sure there is a way to continue using std::filesystem::copy when recursively copying read-only directories. We'll have to migrate to something else instead.

Steps to reproduce (from Mikage build folder):

1. ninja install
2. sudo chmod -R -w /usr/local/share/mikage/nand/title
3. ./source/mikage sm3dl.cci --bootstrap_nand --enable_logging

Observed output:

[FRONTEND] [info] Attempting to open "sm3dl.cci" (create=false)
libc++abi: terminating due to uncaught exception of type std::__1::__fs::filesystem::filesystem_error: filesystem error: in create_directory: Permission denied ["/Users/myuser/.local/share/mikage/data/0004009b/00010402"] ["/usr/local/share/mikage/nand/title/0004009b/00010402"]