Fix camel num-upper boundary handling

[smoelius]

Ths PR fixes a problem affecting numbers/uppercase-letter boundaries in identifiers being converted to camel case.

The following else-if case would apply and force the current character to lowercase only if the previous character was uppercase:

paste/src/segment.rs

Lines 204 to 208 in c71982e

	} else if prev.is_uppercase() {
	for chl in ch.to_lowercase() {
	acc.push(chl);
	}
	} else {

If the previous character was a number, the above case would not apply and the current character would be pushed unchanged:

paste/src/segment.rs

Lines 208 to 210 in c71982e

	} else {
	acc.push(ch);
	}

This would cause an input string like TMPG_M2HH3 to be incorrectly converted to TmpgM2Hh3 (playground).

The proposed fix is to always force lowercase in the else case, i.e., essentially eliminate the if prev.is_uppercase() check.