fix(DataTableToolbar): apply default bottom spacing

[khushal-winner]

Reduces marginBottom from theme.spacing(4) to theme.spacing(2) so consumers inherit the toolbar-to-table gap without per-call-site sx overrides. Callers can still override via sx.

Closes #1719

Notes for Reviewers

This PR fixes #

Signed commits

• Yes, I signed my commits.

Summary by CodeRabbit

• Style
  • Reduced the default spacing below the data table toolbar for a more compact layout.
  • Toolbar spacing overrides now support both top and bottom margins.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 09186f6a-5f5b-47eb-b7c8-c86277f005d1

📥 Commits

Reviewing files that changed from the base of the PR and between e20fd02 and a7c7004.

📒 Files selected for processing (2)

• src/__testing__/DataTableToolbar.test.tsx
• src/custom/DataTableToolbar/DataTableToolbar.tsx

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📝 Walkthrough

Walkthrough

DataTableToolbar now defaults to a 16px bottom margin, while sx values can override both top and bottom margins. Tests cover the updated default and override behavior.

Changes

DataTableToolbar spacing

Layer / File(s)	Summary
Default bottom spacing and overrides src/custom/DataTableToolbar/DataTableToolbar.tsx, src/__testing__/DataTableToolbar.test.tsx	ToolbarRoot uses theme.spacing(2) for marginBottom; tests verify the 16px default and custom marginTop and marginBottom overrides.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: uday9909

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: adding default bottom spacing to DataTableToolbar.
Linked Issues check	✅ Passed	The changes implement the requested default marginBottom spacing and preserve sx overrides as required by #1719.
Out of Scope Changes check	✅ Passed	The PR stays focused on DataTableToolbar spacing and matching tests, with no obvious unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[khushal-winner]

@KhushamBansal , is it good to go?