fix(format/writer): strings longer than the buffer chunk size are written correctly

[Viatorus]

Fixes #68

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (423edc9) 99.40% compared to head (40fffb4) 99.40%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #71 +/- ## ======================================= Coverage 99.40% 99.40% ======================================= Files 56 56 Lines 5866 5869 +3 ======================================= + Hits 5831 5834 +3 Misses 35 35 ``` | [Files](https://app.codecov.io/gh/Viatorus/emio/pull/71?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/writer.hpp](https://app.codecov.io/gh/Viatorus/emio/pull/71?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-aW5jbHVkZS9lbWlvL3dyaXRlci5ocHA=) | `100.00% <100.00%> (ø)` | | | [test/unit\_test/test\_writer.cpp](https://app.codecov.io/gh/Viatorus/emio/pull/71?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Toni+Neubert#diff-dGVzdC91bml0X3Rlc3QvdGVzdF93cml0ZXIuY3Bw) | `100.00% <100.00%> (ø)` | |

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