Optimizations for KeyBuilder

[nan01ab]

Description

Optimizing memory allocation for KeyBuilder and add UTs for not-convered methods

Benchmarks:
Before:

BenchmarkDotNet v0.13.12, macOS 15.1.1 (24B2091) [Darwin 24.1.0]
Apple M4 Pro, 1 CPU, 14 logical and 14 physical cores
.NET SDK 8.0.404
  [Host]     : .NET 8.0.11 (8.0.1124.51707), Arm64 RyuJIT AdvSIMD
  DefaultJob : .NET 8.0.11 (8.0.1124.51707), Arm64 RyuJIT AdvSIMD


| Method                | Mean     | Error    | StdDev   |
|---------------------- |---------:|---------:|---------:|
| KeyBuilder_AddInt     | 40.16 ns | 0.090 ns | 0.084 ns |
| KeyBuilder_AddBytes   | 36.04 ns | 0.051 ns | 0.048 ns |
| KeyBuilder_AddUInt160 | 45.21 ns | 0.044 ns | 0.039 ns |

After:

BenchmarkDotNet v0.13.12, macOS 15.1.1 (24B2091) [Darwin 24.1.0]
Apple M4 Pro, 1 CPU, 14 logical and 14 physical cores
.NET SDK 8.0.404
  [Host]     : .NET 8.0.11 (8.0.1124.51707), Arm64 RyuJIT AdvSIMD
  DefaultJob : .NET 8.0.11 (8.0.1124.51707), Arm64 RyuJIT AdvSIMD


| Method                | Mean     | Error    | StdDev   |
|---------------------- |---------:|---------:|---------:|
| KeyBuilder_AddInt     | 27.27 ns | 0.110 ns | 0.103 ns |
| KeyBuilder_AddBytes   | 27.43 ns | 0.059 ns | 0.056 ns |
| KeyBuilder_AddUInt160 | 25.75 ns | 0.031 ns | 0.029 ns |

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules