Remove unused utility methods and inline remaining contents of Utils.swift

[mattt]

While reviewing #308, I noticed a change from CFAbsoluteTimeGetCurrent to Date().timeIntervalSinceReferenceDate that I wanted to double-check, and noticed that we aren't actually using that anywhere.

This PR removes this and the other unused utility methods in Utils.swift, and inlines the remaining ones.

[Copilot]

Pull request overview

This PR removes the Utils.swift file containing utility methods that are either unused or can be inlined at their call sites. The change simplifies the codebase by eliminating a utility class and directly incorporating the necessary functionality where it's used.

Changes:

• Removed unused utility methods (time, dateNow, clamp, fakeThrowable) from Utils.swift
• Inlined dictionary inversion logic using reduce(into:) at three call sites
• Converted isChineseChar static function to a UnicodeScalar extension property isCJKUnifiedIdeograph
• Inlined substring extraction logic in BertTokenizer's WordpieceTokenizer
• Moved PUNCTUATION_REGEX constant from public Constants enum to a private file-level constant in PreTokenizer.swift

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Sources/Tokenizers/Utils.swift	Entire file removed, eliminating unused utilities and those that have been inlined
Sources/Tokenizers/PreTokenizer.swift	Inlined punctuation regex as a private file-level constant
Sources/Tokenizers/Normalizer.swift	Added UnicodeScalar extension with isCJKUnifiedIdeograph property to replace Utils.isChineseChar
Sources/Tokenizers/ByteEncoder.swift	Inlined dictionary inversion using reduce(into:)
Sources/Tokenizers/BertTokenizer.swift	Inlined dictionary inversion, substring extraction, and updated to use isCJKUnifiedIdeograph extension
Sources/Tokenizers/BPETokenizer.swift	Inlined dictionary inversion using reduce(into:)

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[pcuenca]

Oh nice, thanks for taking the time to double-check and clean up!