fix: add missing types node's children

[bartveneman]

Make WithChildren generic so we can give a narrower subset of what kind of children is possible if a node has children.

[codecov-commenter]

Bundle Report

Changes will increase total bundle size by 1.05kB (0.59%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
@projectwallace/css-parser-esm	181.23kB	1.05kB (0.59%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: @projectwallace/css-parser-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
node-types-De9R2IIL.d.ts (New)	22.41kB	22.41kB	100.0% 🚀
css-node-DwKXZuNm.js (New)	14.17kB	14.17kB	100.0% 🚀
node-types-Dt096ytO.d.ts (Deleted)	-21.37kB	0 bytes	-100.0% 🗑️
css-node-CbNQbD4P.js (Deleted)	-14.15kB	0 bytes	-100.0% 🗑️

Files in css-node-DwKXZuNm.js:

• ./src/css-node.ts → Total Size: 13.96kB

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.50%. Comparing base (c375f50) to head (2188514).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #207   +/-   ##
=======================================
  Coverage   93.50%   93.50%           
=======================================
  Files          17       17           
  Lines        2939     2939           
  Branches      810      810           
=======================================
  Hits         2748     2748           
  Misses        191      191           

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