fix(localedata): don't memoize resolved aliases into shared parent data

[SAY-5]

Fixes #1234.

A locale that inherits an entire nested sub-dict from its parent shares the same dict object (merge only copies keys present in the child's own data). When LocaleDataDict.__getitem__ resolved an Alias and wrote the resolved value back into self._data as a memoization, it mutated that shared dict, corrupting the parent locale (and every sibling that inherits it).

For example he aliases its stand-alone wide months to the Hebrew format months. After format_date(d, 'LLLL', 'he'), a later format_date(d, 'LLLL', 'de') returned Hebrew text because root's shared months/stand-alone/wide Alias had been overwritten.

Fix: skip the write-back memoization when the value came from resolving an alias, since the backing dict may be shared with a parent locale. Plain nested dicts are still wrapped and memoized as before.

Added a regression test.