perf: shorten some print functons && use string concat directly in some places

[bartveneman]

Summary

This PR refactors multiple string-building operations throughout the CSS formatter to use direct string concatenation instead of building arrays and joining them. This simplifies the code and improves readability while maintaining the same functionality.

Key Changes

• print_operator(): Replaced array-based building with direct concatenation using ternary operators to determine spacing rules
• print_declaration(): Changed important from array to string, simplified the logic for extracting and formatting the !important flag
• print_nth(): Replaced parts array with direct string concatenation and template literals
• print_nth_of(): Converted from array building to direct string concatenation
• print_compound_selector(): Simplified to use map().join() instead of manual forEach loop
• print_rule(): Moved block_has_content calculation to the top to avoid duplication, simplified block rendering logic
• print_atrule(): Refactored name building from array to string concatenation, consolidated block_has_content logic to avoid recalculation, simplified return statements

Notable Implementation Details

• All changes maintain the exact same output formatting and CSS specification compliance
• The refactoring reduces intermediate array allocations and simplifies control flow
• Comments explaining CSS specification requirements (e.g., spacing around + and - operators) are preserved

https://claude.ai/code/session_01P6rhwrSj4m7rKSqqsPUqgz

[codecov]

Bundle Report

Changes will decrease total bundle size by 472 bytes (-1.72%) ⬇️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
formatCss-esm	12.93kB	-472 bytes (-3.52%) ⬇️

Affected Assets, Files, and Routes:

view changes for bundle: formatCss-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
index.js	-472 bytes	12.37kB	-3.68%

Files in index.js:

• ./src/lib/index.ts → Total Size: 12.24kB

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.78%. Comparing base (be22838) to head (dcb7d92).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
- Coverage   96.98%   96.78%   -0.21%     
==========================================
  Files           2        2              
  Lines         365      342      -23     
  Branches      124      119       -5     
==========================================
- Hits          354      331      -23     
  Misses         10       10              
  Partials        1        1              

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