Reduce the number of namespaces

The project uses a large number of namespaces, making it difficult to configure `Config` in the IDE with poor automatic namespace import (e.g. VSCode).

In order not to break the files, because the namespace is deleted, we can add empty class to the "removed" namespace (idk how these classes are usually named).

#### Namespaces with public types:
```
BenchmarkDotNet.Jobs
BenchmarkDotNet.Attributes
BenchmarkDotNet.Validators
BenchmarkDotNet.Toolchains
BenchmarkDotNet.Toolchains.Roslyn
BenchmarkDotNet.Toolchains.Results
BenchmarkDotNet.Toolchains.Parameters
BenchmarkDotNet.Toolchains.NativeAot
BenchmarkDotNet.Toolchains.Mono
BenchmarkDotNet.Toolchains.MonoWasm
BenchmarkDotNet.Toolchains.MonoAotLLVM
BenchmarkDotNet.Toolchains.InProcess
BenchmarkDotNet.Toolchains.InProcess.NoEmit
BenchmarkDotNet.Toolchains.InProcess.Emit
BenchmarkDotNet.Toolchains.InProcess.Emit.Implementation
BenchmarkDotNet.Toolchains.DotNetCli
BenchmarkDotNet.Toolchains.CsProj
BenchmarkDotNet.Toolchains.CoreRun
BenchmarkDotNet.Toolchains.CoreRt
BenchmarkDotNet.Running
BenchmarkDotNet.Reports
BenchmarkDotNet.Properties
BenchmarkDotNet.Portability
BenchmarkDotNet.Portability.Cpu
BenchmarkDotNet.Parameters
BenchmarkDotNet.Order
BenchmarkDotNet.Mathematics
BenchmarkDotNet.Loggers
BenchmarkDotNet.Helpers
BenchmarkDotNet.Filters
BenchmarkDotNet.Extensions
BenchmarkDotNet.Exporters
BenchmarkDotNet.Exporters.Xml
BenchmarkDotNet.Exporters.Json
BenchmarkDotNet.Exporters.Csv
BenchmarkDotNet.Environments
BenchmarkDotNet.Engines
BenchmarkDotNet.Disassemblers
BenchmarkDotNet.Diagnosers
BenchmarkDotNet.ConsoleArguments
BenchmarkDotNet.ConsoleArguments.ListBenchmarks
BenchmarkDotNet.Configs
BenchmarkDotNet.Columns
BenchmarkDotNet.Code
BenchmarkDotNet.Characteristics
BenchmarkDotNet.Attributes.Filters
BenchmarkDotNet.Analysers
BenchmarkDotNet.Diagnostics.Windows
BenchmarkDotNet.Diagnostics.Windows.Tracing
BenchmarkDotNet.Diagnostics.Windows.Configs
```