Refactor packaging install pipeline to shared DESTDIR-based library

[rafatosta]

Motivation

• Centralize all installation/build logic so DEB, AppImage and Snap reuse one installation pipeline and avoid duplicated code.
• Ensure the wheel is the single build artifact and that no packaging step installs into the host filesystem by enforcing installs into DESTDIR.
• Make Snapcraft package an already-prepared installation (no rebuild in the snap build step) using plugin: dump and prepare_package.

Description

• Add builders/common/common.sh providing log, build_wheel, install_wheel, project_version, find_qt_dir, install_dictionaries, validate_install and prepare_package, all operating against DESTDIR only.
• Update builders/anylinux-appimage/get-dependencies.sh to source builders/common/common.sh, download dictionaries if missing, set DESTDIR/PREFIX, and call prepare_package instead of building/installing directly into the host.
• Modify builders/anylinux-appimage/make-appimage.sh to consume the prepared AppDir/usr/bin/zapzap executable and remove duplicated installation and dictionary copy logic so it focuses only on quick-sharun/AppImage generation.
• Add builders/deb/build.sh that sources the common library, exports DESTDIR to a package root, runs prepare_package, and then builds a .deb; add builders/snap/snapcraft.yaml using plugin: dump and an override-build that sources builders/common/common.sh, sets DESTDIR=$CRAFT_PART_INSTALL and calls prepare_package; add a small builders/snap/build.sh wrapper to run snapcraft.

Testing

• Performed shell syntax checks with sh -n on builders/common/common.sh, builders/anylinux-appimage/get-dependencies.sh, builders/anylinux-appimage/make-appimage.sh, builders/deb/build.sh and builders/snap/build.sh, which returned no syntax errors.
• Sourced the new library and ran project_version with . builders/common/common.sh; project_version, which printed the package version successfully.
• Attempted to run DESTDIR=/tmp/zapzap-package-test ./builders/deb/build.sh, which exercised the pipeline but failed in this environment because python -Im build (and installer) are not available, and attempts to pip install them failed due to network/proxy restrictions.

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Codex Task