Add maxTokenCount parameter to CountTokens method

[pgroene]

Updated the CountTokens method in Tokenizer.cs to include a maxTokenCount parameter for limiting token counts. Added tests in TiktokenTests.cs and TokenizerTests.cs to verify the new functionality and ensure correct behavior with the maximum token count.

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fixes #7391

[pgroene]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.88%. Comparing base (e3219a9) to head (ab7de4b).
Report is 4 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #7392 +/- ## ======================================= Coverage 68.88% 68.88% ======================================= Files 1473 1473 Lines 270814 270827 +13 Branches 27884 27884 ======================================= + Hits 186553 186572 +19  + Misses 76985 76983 -2  + Partials 7276 7272 -4 

Flag	Coverage Δ
Debug	68.88% <100.00%> (+<0.01%)	⬆️
production	63.19% <100.00%> (+<0.01%)	⬆️
test	89.39% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/Microsoft.ML.Tokenizers/Tokenizer.cs	84.57% <100.00%> (ø)
...est/Microsoft.ML.Tokenizers.Tests/TiktokenTests.cs	99.00% <100.00%> (+0.01%)	⬆️
...st/Microsoft.ML.Tokenizers.Tests/TokenizerTests.cs	99.31% <100.00%> (+0.01%)	⬆️

... and 5 files with indirect coverage changes

[stephentoub]

Adding a parameter like this, even an optional one, is a binary breaking change.

[ericstj]

Adding a parameter like this, even an optional one, is a binary breaking change.

To make this change compatibly it must an overload.

[tarekgh]

We need to be careful though when adding the new overloads because some tokenizers implementing such functionality already

machinelearning/src/Microsoft.ML.Tokenizers/Model/SentencePieceTokenizer.cs

Line 881 in 8611211

public int CountTokens(string text, bool addBeginningOfSentence, bool addEndOfSentence, bool considerPreTokenization, bool considerNormalization, out string? normalizedText, out int charsConsumed, int maxTokenCount = int.MaxValue)

[tarekgh]

@pgroene just curious what tokenizer you are using? and is this a blocking issue for you or can you wait? I am asking to ensure we'll get it right and ensure this is going to work with all tokenizers without any breaking change.

[pgroene]

We are using the tiktokentokenizer.

[tarekgh]

I talked offline to @pgroene and I suggested to him to use the following API which should give him the same result:

public int GetIndexByTokenCount(string text, int maxTokenCount, out string? normalizedText, out int tokenCount, bool considerPreTokenization = true, bool considerNormalization = true

I am closing this PR for now and we already have issue to track adding the other API but it is not a priority now as there is workaround for it.