feat(buffer): provide a truncating buffer

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (9d6508d) 99.38% compared to head (7c658a0) 99.39%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #63 +/- ## ========================================== + Coverage 99.38% 99.39% +0.01% ========================================== Files 56 56 Lines 5681 5825 +144 ========================================== + Hits 5646 5790 +144 Misses 35 35 ``` | [Files](https://app.codecov.io/gh/Viatorus/emio/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert) | Coverage Δ | | |---|---|---| | [include/emio/buffer.hpp](https://app.codecov.io/gh/Viatorus/emio/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-aW5jbHVkZS9lbWlvL2J1ZmZlci5ocHA=) | `99.37% <100.00%> (+0.10%)` | :arrow_up: | | [include/emio/iterator.hpp](https://app.codecov.io/gh/Viatorus/emio/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-aW5jbHVkZS9lbWlvL2l0ZXJhdG9yLmhwcA==) | `100.00% <ø> (ø)` | | | [test/unit\_test/test\_buffer.cpp](https://app.codecov.io/gh/Viatorus/emio/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-dGVzdC91bml0X3Rlc3QvdGVzdF9idWZmZXIuY3Bw) | `100.00% <100.00%> (ø)` | | | [test/unit\_test/test\_format\_to\_api.cpp](https://app.codecov.io/gh/Viatorus/emio/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-dGVzdC91bml0X3Rlc3QvdGVzdF9mb3JtYXRfdG9fYXBpLmNwcA==) | `100.00% <100.00%> (ø)` | |

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