Use `_str_block_width` to calculate title width

[hwmq]

https://github.com/jazzband/prettytable/blob/db4a1e36269792b25c29be76f8ce48969b653c5e/src/prettytable/prettytable.py#L1572

Since title width is currently computed using len, zero-width characters in the title contribute to table width. _str_block_width removes some escape codes before calculating width and returns a more appropriate value. I propose replace len(options["title"]) with _str_block_width(options["title"]).

[hugovk]

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