redo buffer to store more stuff inline in the blocks

I tried it with some 

```
❯ du -ms ../../src/ktexteditor/big.txt
1401    ../../src/ktexteditor/big.txt
❯ wc -l ../../src/ktexteditor/big.txt
26444678 ../../src/ktexteditor/big.txt
```

plain text file. The savings are not that great, given we will now pay with a lot more searching and allocations during runtime after load:

```
peak heap memory consumption:
4,1GB after 07.973s
peak RSS (including heaptrack overhead):
4,3GB
total memory leaked:
2,0MB (367,2kB suppressed)
```

before

```
peak heap memory consumption:
5,0GB after 13.090s
peak RSS (including heaptrack overhead):
5,5GB
total memory leaked:
2,0MB (367,2kB suppressed)
```

now

```
calls to allocation functions:
3.073.507 (367.073/s)
temporary allocations:
1.414.810 (46,03%, 168.972/s)
```

before

```
calls to allocation functions:
23.662.335 (1.569.120/s)
temporary allocations:
98.369 (0,42%, 6.523/s)
```

But that is just after loading, there the 23.662.335 are clear, that is one more per line.