Add ArrayStyle encoder option for multiline arrays

[dereuromark]

Summary

Adds new encoder options for controlling array formatting, useful for better git diffs and readability.

New Options

Option	Type	Default	Description
arrayStyle	ArrayStyle	Inline	Array formatting style
arrayAutoThreshold	int	3	Item count threshold for Auto mode
indent	string	' '	Indentation for multiline arrays

ArrayStyle Enum

• ArrayStyle::Inline - Single line (existing behavior): [1, 2, 3]
• ArrayStyle::Multiline - One item per line with indentation
• ArrayStyle::Auto - Multiline when items exceed threshold

Examples

// Inline (default)
Toml::encode(['ports' => [8080, 8081, 8082]]);
// ports = [8080, 8081, 8082]

// Multiline
Toml::encode(
    ['ports' => [8080, 8081, 8082]],
    new EncoderOptions(arrayStyle: ArrayStyle::Multiline),
);
// ports = [
//     8080,
//     8081,
//     8082,
// ]

// Auto (multiline when > 3 items)
Toml::encode(
    ['ports' => [8080, 8081, 8082, 8083, 8084]],
    new EncoderOptions(arrayStyle: ArrayStyle::Auto, arrayAutoThreshold: 3),
);
// ports = [
//     8080,
//     8081,
//     8082,
//     8083,
//     8084,
// ]

Documentation

Also updates API documentation with complete EncoderOptions reference including previously undocumented options (integerGrouping, trailingComma, dottedKeys).