tokenize: `e.offset` on `IndentationError` is not set correctly

[Sporarum]

Bug report

Bug description:

import io, tokenize

input_s = """
def foo():
    x = 1
   x = "some_very_long_expression"
"""
try:
    list(tokenize.generate_tokens(io.StringIO(input_s).readline))
except IndentationError as e:
    print(f"{e.offset = }")

The line x = "some_very_long_expression" is indented with 3 spaces instead of 4, so we get an error.
We would expect the offset to be around 3, since that is where the issue is.
On python 3.12+, the offset is instead 35, equal to the length of the line + 1.

This appears to be caused by the refactor of tokenize done in 3.12 for PEP 701
Potentially related to #84515
Funnily enough, the exact same thing seems to have happened around 3.8 #75676

Tested versions:

Version	e.offset
3.11.15	3
3.12.13	35
3.13.13	35
3.14.4	35
3.15.0b1	35

Testing command:
nix-shell -p python311 --run "python --version && python tmp.py"
(and replace 311 by 312, 313, etc)

CPython versions tested on:

3.15

Operating systems tested on:

Linux

[picnixz]

I do not know if we can change this because it would create a discrepancy in 3.12 exactly (if we were to backport this) but let us ask our expert @pablogsal

I do agree that it looks like a bug though and that I would like to see it fixed.

[Sporarum]

I do not know if we can change this

This only applies to the backport, for 3.15+ it should still be fixed, right ?

[picnixz]

Yes, AFAICT but maybe the change was deliberate (but I doubt). I just do not know if we can make the change easily (hence my question to Pablo)