Power-of-ten digit-block formatting

When the radix is $10^k$, print the highest nonzero normalized digit without leading zeros, then every lower digit as exactly $k$ decimal characters. Internal zero blocks must be retained. With base $1000$, the low-first digits $[4,0,12]$ print as 12 followed by 000 followed by 004, giving 12000004. An all-zero representation prints a single zero, independent of its allocated length.