Escape locale strings in the from_format pattern

[Sharadhi-v98]

1. from_format joins the locale's month names, day names, day periods and ordinal suffixes into its pattern unescaped, so the dot in abbreviations like "févr." or "Dez." matches any character.
2. The name lookup then returns None, but the guard after it tests value instead of the lookup result, so the month or weekday is dropped and the default is used. pendulum.from_format("15 févrX 2024", "D MMM YYYY", locale="fr") returns 2024-01-15 and "1 juil, 2024" returns 2024-01-01.

Escaped the locale strings and made the guard check the lookup result, so these now raise ValueError.

• Added tests for changed code.
• Updated documentation for changed code.