Support mis-extension-ed JPEGs, skip mis-extension-ed files for exiftool

[ireun]

High level overview:

1. if a file is actually jpeg but with wrong extension:
   use native methods, display a warning
   EDIT: warn only with -v
2. if a file is not actually a jpeg, and has a wrong extention:
   display an error, skip processing - exiftool will fail either way so don't waste time for that.

I might still refactor this, but I want you to take a look. :)

Additionally we need only 96 bytes for header MIME detection. (https://github.com/dart-lang/tools/blob/main/pkgs/mime/lib/src/magic_number.dart has at most 12 HEX values (each has 2 digits) for the header matching -> 12*2*4=96). I've used 128 just in case some future MIME types would require more.

[ireun]

Preview:

[Xentraxx]

I trust you researched the change to 128 bytes, so thats fine!
I'll look at the rest!

[Xentraxx]

Okay looks good and makes sense! Approved.

[ireun]

Next thing to do would be to create a renaming mechanism based on mimeTypeFromHeader, then this whole PR could be removed from code base.

[ireun]

One issue I've found with this:

Some RAW formats (like Canon RAW) are based on TIFF formats. For real .CR2 mimeLookup(path) will return null, while mimeLookup(path, header) will return image/tiff.

I've made PR to add proper mimeLookup() for .CR2 - dart-lang/tools#2105.