Change from file-magic to python-magic, use MAGIC_CONTINUE

[e3krisztian]

MAGIC_CONTINUE is more transparently supported with python-magic.
Also file-magic's last release was in 2018,
while there are recent changes on github.

[e3krisztian]

In Nix pulling in file-magic pulled also libmagic, somehow it does not happen with python-magic :(

[vlaci]

In Nix pulling in file-magic pulled also libmagic, somehow it does not happen with python-magic :(

We did hard work to achieve that https://github.com/onekey-sec/unblob/blob/main/default.nix#L66

[martonilles]

I would extend the commit message explaining why we need neeed MAGIC_CONTINUE or keep_going:

file magic uses a rule-set to guess the file type, however as rules are added they could shadow each other. File magic uses rule priorities to determine which is the best matching rule, however this could shadow other valid matches as well, which could eventually break any further processing that depends on magic.
By enabling keep_going (which eventually enables MAGIC_CONTINUE) all matching patterns will be included in the magic string at the cost of being a bit slower, but increasing accuracy by no shadowing rules.