Optimize English to words converter

[hazzik]

Remove recursion & reduce allocations.

Before:

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4046/22H2/2022Update)
12th Gen Intel Core i7-12800H, 1 CPU, 20 logical and 14 physical cores
.NET SDK 8.0.201
  [Host]     : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2
  DefaultJob : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2

Method	Mean	Error	StdDev	Gen0	Allocated
ToWords	333.2 ns	6.70 ns	19.22 ns	0.1316	1.62 KB
ToWordsOrdinal	366.2 ns	8.01 ns	23.37 ns	0.1349	1.66 KB

After:

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4046/22H2/2022Update)
12th Gen Intel Core i7-12800H, 1 CPU, 20 logical and 14 physical cores
.NET SDK 8.0.201
  [Host]     : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2
  DefaultJob : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2

Method	Mean	Error	StdDev	Gen0	Allocated
ToWords	136.9 ns	2.79 ns	8.13 ns	0.0489	616 B
ToWordsOrdinal	150.0 ns	3.18 ns	9.37 ns	0.0522	656 B