feat: run the steps of another architecture through the host's qemu-user-static

[The127]

A build for the other architecture now uses the qemu-x86_64-static or qemu-aarch64-static that the host's package manager installs. miso no longer downloads a pinned qemu-user package, so QEMU fixes reach users through their package manager, not through a new miso release.

• miso finds the program on PATH. Debian, Fedora and Arch all ship it under these names.
• If it is missing, miso names the qemu-user-static package.
• If it needs a dynamic loader or is built for another machine, miso refuses it with the init's check and names the file.
• The emulator is registered with binfmt_misc under its own path. Upstream QEMU keeps argv[0] through the kernel's P flag, so the Debian-only -binfmt-P name is gone.
• The deb and rpm packages recommend qemu-user-static.

Not tested on real hardware yet: a cross build with a distribution's qemu-user-static.

Docs: I checked them and updated cli.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.13%. Comparing base (5196ee1) to head (4ce691a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
+ Coverage   56.10%   56.13%   +0.03%     
==========================================
  Files         288      288              
  Lines        4761     4756       -5     
==========================================
- Hits         2671     2670       -1     
+ Misses       2090     2086       -4     

Flag	Coverage Δ
unit	56.13% <100.00%> (+0.03%)	⬆️

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