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

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 https://github.com/python/cpython/issues/84515
Funnily enough, the exact same thing seems to have happened around 3.8 https://github.com/python/cpython/issues/75676

Tested versions:

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

Linked PRs

• gh-154281

從 tokenize.generate_tokens 開始，在列出的 Python 版本中重現所提供的 IndentationError 範例。追蹤 tokenizer 如何建構 IndentationError，並將 offset 與 Python 3.11 的行為進行比較。當縮排錯誤的行回報的 offset 接近 3，且該範例具備回歸測試覆蓋時，即表示完成。