fix(realtime): escape quotes and backslashes in in filter values

[AndroidPoet]

What

PostgresChangeFilter.toString() builds the in filter by quoting each value, but never escapes the value first. A value containing a double quote or backslash produces a malformed filter:

PostgresChangeFilter(
  type: PostgresChangeFilterType.inFilter,
  column: 'name',
  value: ['a"b'],
).toString();
// name=in.("a"b")  <-- the inner " breaks the quoted element

This escapes \ and " inside each element before quoting, so the value stays a single well-formed token.

Why

The realtime in filter had the same missing-escaping bug that was fixed for postgrest in #1481 (_cleanFilterArray), but the realtime copy in types.dart was never updated:

return '$column=in.(${value.map((s) => '"$s"').join(',')})';

Any subscription filtering on a list whose values contain " or \ sends a broken filter to the Realtime server. The fix mirrors the PostgREST/PostgreSQL array quoting used by PostgrestFilterBuilder:

final escaped = '$s'.replaceAll(r'\', r'\\').replaceAll('"', r'\"');
return '"$escaped"';

Not a breaking change

Values without " or \ render exactly as before (in.("active","pending")), and non-in filters are untouched. Only previously-malformed output changes.

Tests

Added packages/realtime_client/test/postgres_change_filter_test.dart: asserts ['a"b\c'] renders as name=in.("a\"b\\c"), that plain values are unchanged, and that non-in filters are unaffected. The escaping test fails on the old code (Actual: name=in.("a"b\c")) and passes with the fix. dart format and dart analyze --fatal-warnings are clean.