Fix calc number formatting with digit grouping (bug#36689)
The functions math-format-hex and math-format-octal were not
implemented, yet called, leading to a crash when using hex or octal
radix with digit grouping.
* test/lisp/calc/calc-tests.el (calc-test-format-radix): New test.
* lisp/calc/calc-ext.el: Don't declare non-existing functions.
(math--format-integer-fancy): Don't call non-existing functions.
* lisp/calc/calc-bin.el (math-format-binary, math-binary-digits):
Simplify, fixing 0-padding bug.