Fix packaging on MacOS/Darwin when using native bash v3

[astral303]

Replaces bash 4+ readarray with bash v3-compatible read loops, to allow packaging using native bash on Darwin.

Tested against actual @preview distribution as follows:

$ cd ~/Library/Application\ Support/typst/packages/local && \
    find simple-technical-resume/0.1.1 -type f | xargs sha256sum > /tmp/locally-built-0.1.1.sha256
$ cd ~/Library/Caches/typst/packages/preview  && sha256sum --check /tmp/locally-built-0.1.1.sha256 
simple-technical-resume/0.1.1/typst.toml: OK
simple-technical-resume/0.1.1/LICENSE: OK
simple-technical-resume/0.1.1/CHANGELOG.md: OK
simple-technical-resume/0.1.1/template/main.typ: OK
simple-technical-resume/0.1.1/README.md: OK
sha256sum:  simple-technical-resume/0.1.1/thumbnail.png: No such file or directory
simple-technical-resume/0.1.1/src/resume.typ: OK
simple-technical-resume/0.1.1/src/lib.typ: OK

Not sure why thumbnail.png is missing in the official distribution, as it is not in the .typstignore file, so I can't see any regression or error in logic here.