test: improve coverage for builtin/json.mbt

[rami3l]

Disclaimer: This PR was generated by an LLM agent as part of an experiment.

Summary

coverage of `builtin/json.mbt`: 22.0% -> 97.6%

[peter-jerry-ye-code-review]

‼️ This code review is generated by a bot. Please verify the content before trusting it.

Looking at the git diff output, I've identified a few potential issues:

1. Future Copyright Date: The copyright year is set to 2025 which seems incorrect as it's a future date.

// Copyright 2025 International Digital Economy Academy

2. Inconsistent Type Notation: There's inconsistency in how numeric types are denoted. Some use capital letters (like 42L for Int64 and 42U for UInt) while others use explicit type annotations. This could lead to confusion. For example:

let i : Int64 = 42L
let x = 42U
let num : UInt64 = UInt64::default()

3. Potential Float Precision Issue: In the "test_float_to_json" test, the expected content includes many decimal places for a simple 3.14 value:

inspect!(json_val, content="Number(3.140000104904175)")

This might indicate potential floating-point precision issues that could cause problems in production code where exact decimal representation is important.

These aren't necessarily bugs, but they could lead to maintenance issues or unexpected behavior if not addressed appropriately.

[coveralls]

Pull Request Test Coverage Report for Build 4928

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 83.465%

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Totals
Change from base Build 4921:	0.5%
Covered Lines:	5083
Relevant Lines:	6090

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💛 - Coveralls