Add IntegerType setting to CSharpGeneratorSettings

[Copilot]

CSharpGeneratorSettings had configurable type mappings for numbers, dates, and collections but no equivalent for integer, making it impossible to default to long instead of int globally.

Changes

• CSharpGeneratorSettings: Added IntegerType property (default: "int") alongside the existing numeric type settings
• CSharpTypeResolver.ResolveInteger: Changed from static to instance method; uses Settings.IntegerType as the default fallback (guards against null/whitespace with "int"). Also removed a duplicate long format branch that existed in the original code
• Tests + snapshots: Added two tests covering default int generation and custom type override

Usage

var generator = new CSharpGenerator(schema, new CSharpGeneratorSettings
{
    IntegerType = "long"  // all unformatted integer properties now map to long
});

Note: this setting applies only to integer properties with no explicit format — byte, long (int64 format), and ulong format mappings are unaffected.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support for IntegerType in CSharpGeneratorSettings</issue_title>
<issue_description>We can set several useful default types in CSharpGeneratorSettings, but nothing for integer. Could we get a setting that allows us to use long instead of int by default?</issue_description>

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

• Fixes Support for IntegerType in CSharpGeneratorSettings #1416

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[RicoSuter]

I think we should keep this one, no? Breaking change otherwise.

[lahma]

I think this branch is duplicated just above, so basically removing one of them doesn't matter?