Testing numFormat function:

Basic formatting:
1234.567 -> 1,234.57
0.001234 -> 0
1000000 -> 1,000,000
-42.0 -> −42

With SI exponents:
1234567 with exp 3 -> 1,234.567k
1234567 with exp 6 -> 1.234567M

Different exponent formats:
Format 'e': 1,234.567e+3
Format 'E': 1,234.567E+3
Format 'power': 1,234.567×10<sup>3</sup>
Format 'B': 1,234.567k
Format 'none': 1,234,567
Format 'hide': 1,234.567

Hover mode:
Normal: 1,234.57
Hover:  1,234.567

Negative rounding:
12345 with tickRound -2 -> 12,300

Zero handling:
0 -> 0
0.0001 -> 0
-0.0001 -> 0