Bound pathological addFile() cost by truncating REFS tokenization

[VKspyder2003]

Summary

Limit pathological REFS tokenization by introducing a maximum emitted token count in JFlexTokenizer.

The limit is applied only to the REFS field used for symbol indexing. Other indexing behavior, including FULL, DEFS, xref generation, and metadata indexing, remains unchanged.

Changes

• Add optional emitted-token limit to JFlexTokenizer
• Apply the limit only when indexing the REFS field
• Preserve existing indexing flow and document creation
• Add tokenizer tests
• Add a regression test using the large JavaScript fixture

Fixes #4550

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[VKspyder2003]

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