Add possibility to query solving statistics

[hedtke]

fix #21

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.53%. Comparing base (a946921) to head (654894d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #22 +/- ## ========================================== + Coverage 97.46% 97.53% +0.06% ========================================== Files 8 9 +1 Lines 158 162 +4 Branches 39 39 ========================================== + Hits 154 158 +4 Misses 3 3 Partials 1 1 ``` | [Files](https://app.codecov.io/gh/scipopt/SCIPpp/pull/22?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scipopt) | Coverage Δ | | |---|---|---| | [include/scippp/model.hpp](https://app.codecov.io/gh/scipopt/SCIPpp/pull/22?src=pr&el=tree&filepath=include%2Fscippp%2Fmodel.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scipopt#diff-aW5jbHVkZS9zY2lwcHAvbW9kZWwuaHBw) | `96.15% <100.00%> (+0.32%)` | :arrow_up: | | [include/scippp/statistics.hpp](https://app.codecov.io/gh/scipopt/SCIPpp/pull/22?src=pr&el=tree&filepath=include%2Fscippp%2Fstatistics.hpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scipopt#diff-aW5jbHVkZS9zY2lwcHAvc3RhdGlzdGljcy5ocHA=) | `100.00% <100.00%> (ø)` | |