Add Universal attribute and whitespace sniffs

[dereuromark]

Summary

Covers gaps in the current ruleset for PHP 8 attributes and whitespace — none of these are covered by existing Slevomat/Generic/PSR rules.

Attributes

• `Universal.Attributes.BracketSpacing` — spacing inside `#[…]`
• `Universal.Attributes.DisallowAttributeParentheses` — drop `()` from param-less attributes (`#[Foo]` not `#[Foo()]`)
• `Universal.Attributes.TrailingComma` — trailing comma rules for multi-line attributes

Whitespace

• `Universal.WhiteSpace.AnonClassKeywordSpacing` — spacing after `class` in `new class (…) extends …`
• `Universal.WhiteSpace.FirstClassCallableSpacing` — spacing in `strlen(...)` first-class-callable syntax
• `Universal.WhiteSpace.DisallowInlineTabs` — forbids tabs mid-line (complements existing `Generic.WhiteSpace.DisallowTabIndent` which only covers indent)

Related to #53.

`composer cs-check`, `composer test`, `composer stan` and `composer docs` all pass locally.