Cache and reuse NamedPipeServerStream instances

[JamesNK]

NamedPipeServerStream instances can be reused between connections:

// End connection
_stream.Disconnect();

// Start new connection
await _stream.WaitForConnectionAsync();

This PR adds a cache to the connection listener, allowing streams to be reused between connections.

A further improvement could be to completely reuse NamedPipeConnection (the implementation of ConnectionContext that wraps the stream). However, caching a connection context is harder because it has to determine whether anyone else is still using it. NamedPipeServerStream is private, making it relatively simple to detect whether it is still in use.

Before:

|    Method | ListenerQueueCount |     Mean |    Error |   StdDev |     Op/s | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------- |------------------- |---------:|---------:|---------:|---------:|------:|------:|------:|----------:|
| Plaintext |                  1 | 59.16 us | 1.130 us | 1.257 us | 16,902.9 |     - |     - |     - |     11 KB |
| Plaintext |                  2 | 59.62 us | 1.055 us | 0.935 us | 16,772.6 |     - |     - |     - |     11 KB |
| Plaintext |                  8 | 34.49 us | 0.508 us | 0.450 us | 28,997.5 |     - |     - |     - |     11 KB |
| Plaintext |                 16 | 35.30 us | 0.401 us | 0.335 us | 28,329.2 |     - |     - |     - |     11 KB |

After:

|    Method | ListenerQueueCount |     Mean |    Error |   StdDev |     Op/s | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------- |------------------- |---------:|---------:|---------:|---------:|------:|------:|------:|----------:|
| Plaintext |                  1 | 44.40 us | 0.644 us | 0.602 us | 22,522.2 |     - |     - |     - |      9 KB |
| Plaintext |                  2 | 29.90 us | 0.488 us | 0.433 us | 33,449.5 |     - |     - |     - |      9 KB |
| Plaintext |                  8 | 24.09 us | 0.219 us | 0.194 us | 41,509.1 |     - |     - |     - |      9 KB |
| Plaintext |                 16 | 23.98 us | 0.249 us | 0.221 us | 41,706.7 |     - |     - |     - |      9 KB |

(update) ObjectPool:

|    Method | ListenerQueueCount |     Mean |    Error |   StdDev |     Op/s | Gen 0 | Gen 1 | Gen 2 | Allocated |
|---------- |------------------- |---------:|---------:|---------:|---------:|------:|------:|------:|----------:|
| Plaintext |                  1 | 43.11 us | 0.714 us | 0.668 us | 23,199.0 |     - |     - |     - |      9 KB |
| Plaintext |                  2 | 29.24 us | 0.403 us | 0.377 us | 34,204.9 |     - |     - |     - |      9 KB |
| Plaintext |                  8 | 23.53 us | 0.366 us | 0.343 us | 42,503.3 |     - |     - |     - |      9 KB |
| Plaintext |                 16 | 23.74 us | 0.349 us | 0.326 us | 42,128.1 |     - |     - |     - |      9 KB |