Add input: attribute prefix for targeting the input element

[joshhanley]

The Scenario

When using flux:input, classes and attributes need to be targeted to the inner <input> element rather than the wrapper <div>. Previously, this was only possible using the class:input syntax, which is inconsistent with the nested:attribute convention used by other Flux components (e.g., field:class, label:class, container:class).

<flux:input class="max-w-xs" input:class="text-green-500!" placeholder="Name" />

<flux:input label="Email" input:class="text-green-500!" />

The Problem

The input component only supported the legacy class:input syntax for targeting classes to the <input> element. Other components use the nested:attribute prefix convention (e.g., field:class, label:class, container:class), but the input component didn't support input:class or other input:* attributes.

The Solution

Added support for the input: attribute prefix using the same Flux::attributesAfter() pattern used throughout the codebase. Any input:* attributes are extracted and merged onto the <input> element. The existing class:input syntax continues to work for backwards compatibility.