Implement Report Server ID (function code 17)

[snejugal]

This MR implements the Report Server ID function (code 17) from the spec.

I tried to work around the absence of this function using Custom requests and responses, but it turns out tokio-modbus does not support them properly. Since this function is defined in the spec, I decided to add native support for this function.

[uklotzde]

Welcome and thank you for contributing!

If you have ideas on how to improve the situation around Custom function calls please also consider to submit a PR.

[uklotzde]

Please ignore the pre-commit failure. I'll take care of that separately.

After merging #275 this should be fixed.

[uklotzde]

Merging main will fix the pre-commit failure.

[snejugal]

Rebased on main, the precommit check should pass now.

As of support for custom functions, I think that a trait-based solution might be useful, though that will be a massive overhaul of the crate. Nonetheless, I will try to describe this idea in #123 so it can get some feedback before being implemented (by me or by someone else).

[uklotzde]

In most cases you don't need to rebase. This would invalidate previous review comment. Each PR will be squashed into a single commit when merged.

[uklotzde]

As of support for custom functions, I think that a trait-based solution might be useful, though that will be a massive overhaul of the crate.

Both the public API and the internal implementation could be improved and optimized in many ways.

[uklotzde]

Technically this is a breaking change because FunctionCode is not marked as non_exhaustive (which should probably be added). But I tend to release it as v0.14.1.

Opinions?

[uklotzde]

The breaking change only affects the (experimental) server-side API. Another reason why this should not be bundled in a single crate together with the client-side API.