Add tests for validateDimensions

[Copilot]

Adds 26 test cases covering all validation paths in validateDimensions: valid inputs, boundary conditions (zero, infinity, NaN), threshold violations, and custom validation limits.

Changes

• src/lib_test.ts: Test suite with inline function copy (JSR registry dependency avoidance)
• src/README_TESTS.md: Coverage documentation and edge case notes
• deno.json: Added test task

Coverage

// Zero/invalid values
validateDimensions({ width: 0, height: 100 })
// ["Tile dimensions cannot be zero"]

validateDimensions({ width: NaN, height: 100 })
// ["Tile dimensions resulted in infinity"]

// Threshold violations
validateDimensions({ width: 2001, height: 100 })
// ["Tile width (2001px) exceeds maximum of 2000px"]

// Custom limits
validateDimensions({ width: 3000, height: 3000, validWidth: 5000 })
// []

Notes

Error message "resulted in infinity" applies to both Infinity and NaN values (both fail isFinite() check). Documented as potential improvement area.

Warning

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Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tests for validateDimensions</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add tests for validateDimensions #14

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