fix: don't render an empty paragraph when the callout body is empty

[r4ai]

fix #134

Fixed the issue where an empty paragraph was rendered when the callout body was empty. As a result, empty paragraphs will no longer be rendered for callouts without a title.

For insance,

> [!note]

yieds:

before:

<div data-callout data-callout-type="note">
  <div data-callout-title>Note</div>
  <div data-callout-body>
    <p></p>
  </div>
</div>

after:

<div data-callout="" data-callout-type="note">
  <div data-callout-title="">Note</div>
  <div data-callout-body="">
  </div>
</div>

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: bb837e11e16e20f6559991b8be4add336c97f127

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | -------------------- | ----- | | @r4ai/remark-callout | Minor |

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files	Coverage Δ
packages/remark-callout/src/plugin.ts	98.01% <100.00%> (+0.06%)	:arrow_up: