This is mainly done by avoiding creating additional `StringBuilder`s and writing direct to the `TextWriter` where possible.
Where `StringBuilder`s are still needed, they're pooled and reused

Saves on the amount of allocated memory and time paused for GC.

## Before

> - CommandLine: "s:\ReportGenerator\src\Playground\bin\Debug\net8.0\Playground.exe"
> - Runtime Version: V 8.0.824.36612
> - CLR Startup Flags: 8388611
> - Total CPU Time: 38,443 msec
> - Total GC CPU Time: 1,666 msec
> - Total Allocs : 8,378.712 MB
> - Number of Heaps: 1
> - GC CPU MSec/MB Alloc : 0.199 MSec/MB
> - Total GC Pause: 2,567.9 msec
> - % Time paused for Garbage Collection: 8.1%
> - % CPU Time spent Garbage Collecting: 4.3%
> - Max GC Heap Size: 335.820 MB
> - Peak Process Working Set: 395.698 MB
> - Peak Virtual Memory Usage: 2,480,960.369 MB

## After

> - CommandLine: "s:\ReportGenerator\src\Playground\bin\Debug\net8.0\Playground.exe"
> - Runtime Version: V 8.0.824.36612
> - CLR Startup Flags: 8388611
> - Total CPU Time: 28,247 msec
> - Total GC CPU Time: 1,183 msec
> - Total Allocs : 2,938.748 MB
> - Number of Heaps: 1
> - GC CPU MSec/MB Alloc : 0.403 MSec/MB
> - Total GC Pause: 1,348.8 msec
> - % Time paused for Garbage Collection: 6.2%
> - % CPU Time spent Garbage Collecting: 4.2%
> - Max GC Heap Size: 352.258 MB
> - Peak Process Working Set: 417.976 MB
> - Peak Virtual Memory Usage: 2,480,959.902 MB