test: cover statistics template time defaults

[vycdev2]

Summary

• Extract statistics template rendering into a small testable utility without changing runtime behavior.
• Add regression coverage for zero-duration time tokens, populated values, non-time tokens, repeated tokens, and unsupported placeholders.

Verification

• npm run compile — passed: webpack development bundle built successfully.
• npm test — passed: 233 tests.
• npm run format:check — passed: all matched files use Prettier style.
• git diff --check upstream/develop...HEAD — passed.

Risk

• Low: this is a behavior-preserving extraction with focused regression tests for the existing fix discussed in Change the default value of some statistics tokens to 0 rather than an empty string #78.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.