support 128 bit integers

[tayloraswift]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @tayloraswift, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces support for 128-bit integers (Int128 and UInt128) within the JSON encoding and decoding framework. It modifies the JSON.Number type to accommodate larger integer values by falling back to a string representation when necessary. Additionally, it includes updates to the testing suite to ensure the correct handling of these larger integer types, as well as marking some initializers as deprecated.

Highlights

• Int128 Support: Adds Int128 and UInt128 types to the JSON encoding and decoding conformances, allowing for larger integer values to be represented in JSON.
• JSON.Number Improvements: Modifies JSON.Number to handle larger integer values by using a fallback to string representation when the value exceeds the capacity of UInt64.
• Deprecation: Marks the JSON.Number.Inline initializer as deprecated, recommending direct initialization of JSON.Number instead.
• Test Updates: Updates IntegerOverflow tests to use throws and adds new tests for Int128 and UInt128 roundtripping.

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[gemini-code-assist]

Code Review

This pull request introduces support for 128-bit integers by adding a fallback mechanism to store large numbers as strings, which is a robust approach. The implementation is well-executed, with corresponding updates to initializers and conversion methods. The accompanying tests are thorough, covering new Int128 and UInt128 types, including round-tripping and overflow scenarios. Additionally, there are numerous stylistic improvements that enhance code conciseness. I have a couple of minor suggestions to further improve code clarity.