fix: Set default limit for String column display to 30 and fix edge cases

[stinodego]

Closes #15839

Changes

• Set the default character limit for displaying String columns to 30
  • For DataFrames, changed from 32 to 30
  • For Series, changed from 15 to 30
• Do not count quotes surrounding the value towards the character limit
• Update the HTML repr (Notebooks) to match.
• Make sure Categorical/Enum types follow the same rules (was already the case in the HTML repr).

Example

import polars as pl

with pl.Config(fmt_str_lengths=4):
    print(pl.Series(["abc", "abcd", "abcde"]))

shape: (3,)
Series: '' [str]
[
        "abc"
        "abcd"
        "abcd…    <- note: no trailing quote
]

[codecov]

Codecov Report

Attention: Patch coverage is 95.65217% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 81.26%. Comparing base (f1846a9) to head (8858a62).

Files	Patch %	Lines
crates/polars-core/src/fmt.rs	97.22%	1 Missing ⚠️
py-polars/src/series/mod.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15934   +/-   ##
=======================================
  Coverage   81.25%   81.26%           
=======================================
  Files        1381     1381           
  Lines      176597   176602    +5     
  Branches     3028     3028           
=======================================
+ Hits       143496   143508   +12     
+ Misses      32620    32613    -7     
  Partials      481      481           

Flag	Coverage Δ
python	74.69% <95.65%> (+<0.01%)	⬆️
rust	78.38% <93.47%> (+<0.01%)	⬆️

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[Julian-J-S]

Very nice, thanks! 🙏🏻