Fix "Snapshot missing" errors caused by unstable Livewire keys in the comment list

[ItsMalikJones]

Fixes #72.

Problem

comment-list.blade.php keyed each child <livewire:dynamic-component> by
$comment->getContentHash(). For a Comment, getContentHash() returns
md5(body + reaction ids), which has two failure modes:

1. Unstable — the hash changes whenever a comment is edited or reacted to,
   so the keyed component effectively re-keys itself mid-lifecycle.
2. Collision-prone — two comments with identical content produce the same
   hash, so they share a wire:key.

Either case breaks Livewire's DOM reconciliation and surfaces as
Snapshot missing on Livewire component errors.

Reproduce: post two comments with identical bodies, or edit / react to an
existing comment in a list — the component throws "Snapshot missing".

Fix

Key each component by $comment::class . ':' . $comment->getId():

• Stable — neither the class nor the primary key changes when a comment is
  edited or reacted to.
• Unique per row — getId() returns the primary key.
• Namespaced by type — prefixing with the class prevents a Comment and a
  RenderableComment that happen to share a numeric id from colliding. This is
  a real scenario when getComments() is overridden to merge non-comment items
  into the list.

Deprecation

getContentHash() is no longer used anywhere in the package. It is marked
@deprecated on the Contracts\RenderableComment interface and both
implementations (Comment, RenderableComment). It is not removed — it is
part of the public contract, so removal is deferred to a future major version.

Tests

Three tests added to tests/Livewire/CommentListTest.php:

• renders duplicate-content comments without key collision — two comments with
  identical bodies render distinct keys.
• keeps comment keys stable across edits — a comment's key is unchanged after
  its body is edited.
• renders Comment and RenderableComment sharing an id without key collision —
  a Comment and a RenderableComment with the same id render distinct keys.

Backwards compatibility

No breaking changes. The wire:key value format is internal to Livewire's
rendering and is not a public API. getContentHash() remains callable
(deprecated only).