Improve APT retry logic to handle failures caused by by-hash/CDN issues. Both misc/build.func and misc/install.func now write an apt config to disable Acquire::By-Hash, remove /var/lib/apt/lists/* and retry apt-get update/install; if that still fails they substitute deb.debian.org with ftp.debian.org as a fallback. This makes container builds and package updates more robust against CDN/hash-related apt failures.
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