feat(Rust): Add integer type inference option

[jonashao]

Description

This PR introduces integer type inference for Rust targets, providing better control over generated integer types (i32/i64):

1. Added IntegerType enum with variants:

   • conservative: Selects i32/i64 based on JSON sample ranges
   • force-i32: Always uses i32 (caution: risk of overflow)
   • force-i64: Default behavior (current output)

2. Added integerType configuration option for CLI and programmatic interfaces:

   quicktype --integer-type conservative  # Smart selection (default)
   quicktype --integer-type force-i32

Related Issue

#2790
(Original feature request: #2790)

Motivation and Context

• ⚠️ Problem: Current behavior always generates i64 even when values fit in i32, causing:
  • Memory bloat (4-byte vs 8-byte overhead)
  • Compatibility issues with Rust libraries expecting i32
  • Serialization/deserialization performance penalties
• ✅ Solution: Gives users control to optimize for:
  • Memory efficiency (force-i32)
  • Safety (force-i64)
  • Smart balancing (conservative)

Previous Behaviour / Output

All integers unconditionally became i64:

// JSON schema input:  {"id": {"type": "integer","minimum": 0, "maximum": 100}}
pub struct Data {
    pub id: i64,  // ← Always i64 even for small values
}

New Behaviour / Output

With --integer-type conservative:

// JSON schema input: {"id": {"type": "integer","minimum": 0, "maximum": 100}, "big": {"type": "integer","minimum": 0, "maximum": 9223372036854775807}}
pub struct Data {
    pub id: i32,   // ← conservative-downgraded to i32
    pub big: i64,  // ← Remains i64 for large values
}

How Has This Been Tested?

1. Unit Tests:

   • Added integer-type.schema test input and rust langauge quickTestRendererOptions:
     • Range detection logic (conservative mode)
     • Forced type behaviors (force-i32/force-i64)
   • Integration tests for CLI flag parsing

2. Validation Tests:

   # Tested with sample datasets:
   script/quicktype -s schema test/inputs/schema/integer-type.schema -o out.rs 
   script/quicktype -s schema test/inputs/schema/integer-type.schema -o out.rs  --integer-type force-i32
   script/quicktype -s schema test/inputs/schema/integer-type.schema -o out.rs  --integer-type force-i64

   • Verified output compiles with cargo check

3. Environment:

   • Rust 1.87 + TypeScript 5.0
   • Windows/Linux/macOS cross-validation