Add docker support

docker/8.1-alpine/Dockerfile

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+FROM php:8.1-alpine
+
+# Install os-level dependencies
+RUN apk update \
+    && apk --no-cache --virtual add git pcre-dev ${PHPIZE_DEPS}
+
+# Install scalar extension
+RUN git clone https://github.com/nikic/scalar_objects.git \
+    && cd scalar_objects \
+    && phpize \
+    && ./configure --enable-scalar_objects \
+    && make \
+    && make install \
+    && php run-tests.php -p `which php` --show-diff -d extension=`pwd`/modules/scalar_objects.so -q \
+    && docker-php-ext-enable scalar_objects
+
+# Remove os-level dependencies and src code
+RUN apk del git pcre-dev ${PHPIZE_DEPS} \
+    && rm -rf scalar_objects \
+    && apk del git pcre-dev ${PHPIZE_DEPS} \
+    && rm -rf /tmp/* /var/tmp/*
+
+ENTRYPOINT ["docker-php-entrypoint"]
+CMD ["php", "-a"]

docker/8.1-cli/Dockerfile

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+FROM php:8.1-cli 
+
+# Install os-level dependencies
+RUN apt-get update && apt-get install -y git
+
+# Install scalar extension
+RUN git clone https://github.com/nikic/scalar_objects.git \
+    && cd scalar_objects \
+    && phpize \
+    && ./configure --enable-scalar_objects \
+    && make \
+    && make install \
+    && php run-tests.php -p `which php` --show-diff -d extension=`pwd`/modules/scalar_objects.so -q \
+    && docker-php-ext-enable scalar_objects
+
+# Delete src code and os-level dependencies
+RUN rm -rf scalar_objects \
+    && apt-get purge -y git \
+    && apt-get clean -y \
+    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+ENTRYPOINT ["docker-php-entrypoint"]
+CMD ["php", "-a"]

docker/README.md

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+# Docker images
+
+Use `nikic/scalar_objects` with docker
+
+# Steps
+
+1. Build your image
+```shell
+$ docker build -t php-scalar-objects ./8.1-alpine
+```
+
+2. Create a docker file for your projects
+
+Example `Dockerfile`
+```dockerfile
+FROM php-scalar-objects
+COPY . /usr/src/myapp
+WORKDIR /usr/src/myapp
+CMD [ "php", "./index.php" ]
+```
+
+Example `index.php`
+```php
+<?php
+
+class StringHandler
+{
+    public static function length($self)
+    {
+        return strlen($self);
+    }
+
+    public static function startsWith($self, $other)
+    {
+        return strpos($self, $other) === 0;
+    }
+}
+
+register_primitive_type_handler('string', 'StringHandler');
+
+$string = "abc";
+var_dump($string->length()); // int(3)
+var_dump($string->startsWith("a")); // bool(true)
+```
+
+3. Build your project
+
+```shell
+$ docker build -t my-php-app .
+```
+
+> Execute this in the same directory where your app is
+
+4. Run your app
+
+```shell
+$ docker run -it --rm --name my-php-running-app my-php-app:latest
+```