fractions: Should we support unicode in width/precision formatting fields?

Bug report

Bug description:

Currently, specification allows only [0-9] digits. Though, actual implementation permits unicode symbols for float/Decimal's, but not Fraction's:

>>> f"{decimal.Decimal('123'):.١١f}"  # arabic 11 in precision
'123.00000000000'
>>> f"{fractions.Fraction('123'):.١١f}"
Traceback (most recent call last):
  File "<python-input-9>", line 1, in <module>
    f"{fractions.Fraction('123'):.١١f}"
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Lib/fractions.py", line 600, in __format__
    raise ValueError(
    ...<2 lines>...
    )
ValueError: Invalid format specifier '.١١f' for object of type 'Fraction'
>>> f"{float(fractions.Fraction('123')):.١١f}"
'123.00000000000'

Quick tests shows no measurable performance penalty with unicode support:

$ python -m timeit -s 'from fractions import Fraction as F' 'format(F(123), ".11f")'
10000 loops, best of 5: 39.2 usec per loop
$ python -m timeit -s 'from fractions import Fraction as F' 'format(F(123), ".١١f")'  # with patch
5000 loops, best of 5: 40.2 usec per loop

diff --git a/Lib/fractions.py b/Lib/fractions.py
index 063f28478c..b4120b2beb 100644
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -170,7 +170,7 @@ def _round_to_figures(n, d, figures):
     (?P<zeropad>0(?=[0-9]))?
     (?P<minimumwidth>0|[1-9][0-9]*)?
     (?P<thousands_sep>[,_])?
-    (?:\.(?P<precision>0|[1-9][0-9]*))?
+    (?:\.(?P<precision>0|\d*))?
     (?P<presentation_type>[eEfFgG%])
 """, re.DOTALL | re.VERBOSE).fullmatch

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-140654

Review the format-specification regex in Lib/fractions.py and the linked PR gh-140654 first. Reproduce the Arabic-digit precision examples for Fraction, Decimal, and float, then compare the result with the documented format specification. Done means Fraction accepts the intended Unicode precision syntax consistently.