Bazel: Define a minimal Bazel module

[egorich239]

This defines the very minimal integration with Bazel build system. The definitions follow the spirit of README.md in that the build rules package the library such that it can be included with

#include <spng.h>

[randy408]

I'm not familiar with bazel, does this specify 1.3.1 and only 1.3.1 or the minimum version?

[egorich239]

If libspng is the only user of zlib in a bazel workspace, then it would mean 1.3.1 exactly.
If there is another bazel_dep with, say, zlib 1.3.2 in its dependencies, then

• if 1.3.1 and 1.3.2 have the same compatibility_level in their definition (here: https://github.com/bazelbuild/bazel-central-registry/blob/main/modules/zlib/1.3.1/MODULE.bazel#L4 ), the later 1.3.2 version is pulled;
• otherwise, the dependency graph cannot be resolved.

Full details:

• https://bazel.build/external/module#version-selection
• https://bazel.build/external/module#compatibility_level