diff fails on apks: can't make X relative to Y

[tstromberg]

mal diff py3.13-debugpy-1.8.7-r0.apk py3.13-debugpy-1.8.8-r0.apk generates the following error

💣 rel("py3.13-debugpy-1.8.7-r0.apk","/private/var/folders/gw/86t1jg2109s5j8vzszj281kc0000gn/T/py3.13-debugpy-1.8.7-r0.apk3113364428/usr/lib/python3.13/site-packages/debugpy/__main__.py"):
Rel: can't make /private/var/folders/gw/86t1jg2109s5j8vzszj281kc0000gn/T/py3.13-debugpy-1.8.7-r0.apk3113364428/usr/lib/python3.13/site-packages/debugpy/__main__.py relative to py3.13-debugpy-1.8.7-r0.apk

My guess is it will also fail against other archive formats.

Reported by @imjasonh

[egibs]

Quick test on two APKs in the same directory:

$HOME/go/1.23.2/bin/mal diff py3.13-debugpy-bin-1.8.6-r1.apk py3.13-debugpy-bin-1.8.7-r0.apk
├─ 🔵 Deleted: ../py3.13-debugpy-bin-1.8.6-r1.apk ∴ /usr/bin/debugpy [LOW]
│     ≡ filesystem [LOW]
│       🔵 path/usr_bin — path reference within /usr/bin: /usr/bin/python3.13
│
├─ 🔵 Added: ../py3.13-debugpy-bin-1.8.7-r0.apk ∴ /usr/bin/debugpy [LOW]
│     ≡ filesystem [LOW]
│       🔵 path/usr_bin — path reference within /usr/bin: /usr/bin/python3.13
│
├─ 🟡 Moved: ../py3.13-debugpy-bin-1.8.6-r1.apk ∴ /var/lib/db/sbom/py3.13-debugpy-bin-1.8.6-r1.spdx.json -> py3.13-debugpy-bin-1.8.7-r0.apk ∴ /var/lib/db/sbom/py3.13-debugpy-bin-1.8.7-r0.spdx.json (score: 0.973626)
│

The curious thing here is that identical file names are showing as deleted/added instead of modified.

[egibs]

Ah, I see why. This is from the clean path changes for archives in #617. I'll work on handling this differently for diffs.