Maintenance updates to enable new releases

[mike42]

Fixing a bunch of things to get us up to a maintainable state, per #1396 plus some things I've found along the way.

• Dropping support for PHP < 8.2 - this is a breaking change which will require a major version increment
• Dropping Travis CI and coveralls builds
• Introducing GitHub actions, testing 8.2, 8.3, 8.4 and 8.5
• Updating gfx-php, our image processing dependency, where I went through this process recently (see v1.0)
• Updating PHPUnit (strongly tied to PHP versions)
• Fixing tests well enough that we can see that the library vaguely works on these versions
• Updating badges in the README
• Fixing PHP implied nullable argument deprecation warnings, which is the main reason we need to do a new release
• A modernization pass over the code to introduce strict types, plus many type hints. There is no plan to intentionally change the API, but this may technically be a breaking change
• Updates to copyright notice
• Inclusion of a .gitattributes file to exclude test data from the distributed package

[mike42]

Currently getting failures on one test on PHP 8.5 only, looking at it.

1) CodePageTest::testDataGenerateFailed
IntlException: UConverter::__construct(): returned error 4: U_FILE_ACCESS_ERROR

Fixed: Confirmed that this is a PHP 8.5 change - it now throws if an unknown code page is passed to UConverter.

[erikn69]

• Remove config.platform.php for testing dependency resolution, Ignore composer.lock #1398

I think these changes are necessary.

Maybe example folder must be in .gitattributes with export-ignore

[mike42]

Thanks for picking up that typo @erikn69 - I've grabbed a few changes from your PR #1398

A few notes-

• Inclusion of the lockfile and version override are intentional to help with development. It does not affect the production install.
• I was 50/50 on bundling examples. I decided to leave them in for now, because it helps with bug tracker traffic if corresponding examples / known-good test images are easily available to new users.
• Re BUG: Support \t, \r on raw usage, they are printable #1355, that doesn't relate to getting the code up and running on more modern PHP versions, I'll leave that for now.

[mike42]

This package has a good test suite, but to make sure everything is installable, I ran a test locally using 4 PHP versions (via docker) and a real printer.

I added this dev branch to a blank project like this:

php composer.phar init --no-interaction --name foooo
php composer.phar require --no-interaction mike42/escpos-php:dev-1396-maintenance-updates

Ran this test script:

<?php
require __DIR__ . '/vendor/autoload.php';
use Mike42\Escpos\PrintConnectors\FilePrintConnector;
use Mike42\Escpos\Printer;
$connector = new FilePrintConnector("out.bin");
$printer = new Printer($connector);
$printer -> text("Hello from ".PHP_VERSION."!\n");
$printer -> cut();
$printer -> close();
EOF

And then collected the output files and sent them to an Epson TM-T20III printer to test, using cat out-*.bin | sudo tee /dev/usb/lp0.