Reduce string allocations when writing documents

[lahma]

string.Format is a bad thing in hot paths. Changed code to call multiple Writes instead of string concatenation.

NPOI.Benchmarks.LargeExcelFileBenchmark

Diff	Method	Mean	Error	Allocated
Old	Load	11.741 s	1.1257 s	3.65 GB
New		11.626 s (-1%)	2.0913 s	3732.62 MB (0%)
Old	Write	3.483 s	0.1738 s	1.19 GB
New		3.058 s (-12%)	0.2296 s	611.83 MB (-50%)
Old	Evaluate	62.677 s	4.1891 s	75.32 GB
New		64.658 s (+3%)	24.1520 s	77128.7 MB (0%)

NPOI.Benchmarks.RangeValuesBenchmark

Diff	Method	Mean	Error	Allocated
Old	Double	85.46 ms	0.367 ms	31.45 MB
New		82.83 ms (-3%)	0.382 ms	26.98 MB (-14%)
Old	String	99.93 ms	0.449 ms	59.32 MB
New		91.75 ms (-8%)	0.803 ms	53.92 MB (-9%)
Old	Date	114.71 ms	1.603 ms	35.73 MB
New		108.22 ms (-6%)	0.239 ms	30.55 MB (-14%)
Old	Formulas	1,064.12 ms	10.889 ms	1480.15 MB
New		1,057.00 ms (-1%)	4.548 ms	1473.42 MB (0%)

[tonyqus]

LGTM

[tonyqus]

I'm checking if we can rewrite serialization part with https://github.com/Cysharp/ZString.

According to nuget stats, this library looks popular.

I found this library via this post

[lahma]

I can recommend that library, Orchard Core for example uses that, got a PR approved once to that lib Cysharp/ZString#50 .