fix: bound agentflow token counting fallback

[vicksiyi]

Summary

• Added a bounded token counter with approximate fallback and reused it in agentflow summary-buffer memory paths.

Tests

• git diff --check passed
• ./node_modules/.bin/jest nodes/agentflow/utils.test.ts --runInBand --verbose passed
• ./node_modules/.bin/tsc --noEmit --pretty false passed from packages/components
• prettier check passed
• eslint blocked locally by Node v26 ERR_INVALID_PACKAGE_CONFIG

Notes

• Related issue: Condition Agent nodes hang 15+ seconds on tiktoken.pages.dev DNS failure - need graceful fallback #5546

[gemini-code-assist]

Code Review

This pull request introduces a robust token counting utility (createTokenCounter) with timeout handling and fallback mechanisms, integrating it across several agent flow nodes to manage memory limits safely. The feedback suggests addressing a potential timeout leak in getNumTokensWithTimeout if a synchronous error is thrown, and adding defensive checks in createTokenCounter to handle nullish or invalid llm objects.

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