BPE Tokenizer doesn't allow reading carriage return symbol

**System Information (please complete the following information):**
- OS & Version: windows 11
- ML.NET Version: [0.20.1](https://www.nuget.org/packages/Microsoft.ML.Tokenizers/0.20.1)
- .NET Version: .NET 7

**Describe the bug**
BPE Tokenizer doesn't allow reading carriage return symbol.
https://github.com/dotnet/machinelearning/blob/077a6b81966dc2c514572568917f36cb94e08ac4/src/Microsoft.ML.Tokenizers/Model/BPE.cs#L297
Reading text with ReadLines causes inability to read the carriage return symbol in merges.

**To Reproduce**
Steps to reproduce the behavior:
```csharp
using System.Text.Json;
using Microsoft.ML.Tokenizers;

var vocabFilePath = @"vocab.json";
var mergeFilePath = @"merges.txt";
try
{
var tokenizer = new Tokenizer(new Bpe(vocabFilePath, mergeFilePath, ""));

var input = " Test String ";

var tokenizerEncodedResult = tokenizer.Encode(input);
Console.WriteLine(JsonSerializer.Serialize(tokenizerEncodedResult.Ids));
var tokenizerDecodedResult = tokenizer.Decode(tokenizerEncodedResult.Ids);
Console.WriteLine(tokenizerDecodedResult);
}
catch (Exception e)
{
Console.WriteLine(e);
}
```

```
System.InvalidOperationException: Invalid merger file format at line: 3869
at Microsoft.ML.Tokenizers.Bpe.ConvertMergesToHashmap(String mergesFile)
at Microsoft.ML.Tokenizers.Bpe.ReadFile(String vocab, String merges)
at Microsoft.ML.Tokenizers.Bpe..ctor(String vocabFile, String mergesFile, String unknownToken, String continuingSubwordPrefix, String endOfWordSuffix)
at Program.$(String[] args) in D:\dev\personal\ai\Program.cs:line 8
```

**Expected behavior**
BPE should process merges without exception

**Simple solution**
Read a json instead
```csharp

internal static Vec<(string, string)> ConvertMergesToHashmap(string? mergesFile)
{
if (mergesFile is null)
{
return new Vec<(string, string)>();
}

Vec<(string, string)> merges = new(1000);

int lineNumber = 0;
List mergesList;
using (Stream stream = File.OpenRead(mergesFile))
{
mergesList = JsonSerializer.Deserialize>(stream);
}
foreach (string line in mergesList)
{
lineNumber++;
if (line.StartsWith("#version", StringComparison.Ordinal) || line.Length == 0)
{
continue;
}
int index = line.IndexOf(' ');
if (index < 0 || index == line.Length - 1 || line.IndexOf(' ', index + 1) >= 0)
{
throw new InvalidOperationException($"Invalid merger file format at line: {lineNumber}");
}
merges.Push((line.Substring(0, index), line.Substring(index + 1)));
}

return merges;
}
```

**Additional context**
I was able to fix the exception. However, BPE algorithm generates different results in comparison to google's sentencepiece that is widely used in ML.

Start in src/Microsoft.ML.Tokenizers/Model/BPE.cs at ConvertMergesToHashmap, around line 297, and reproduce the failure with the Windows-style merges.txt described in the issue. Verify that carriage-return-containing merge entries are processed without the reported invalid-format exception, then check tokenization results against the expected behavior and the noted SentencePiece difference.

Written by the indexing model from the issue text.