Add support for the Querydsl IN operator in LdapSerializer.

[Ashish-CodeJourney]

Closes #82

Using a Querydsl predicate on a multi-valued attribute, e.g.:

QPerson person = QPerson.person;
repository.findAll(person.studentAliases.contains(alias));

fails with:

java.lang.UnsupportedOperationException: Unsupported operator IN
at org.springframework.data.ldap.repository.support.LdapSerializer.visit(LdapSerializer.java:99)

Querydsl translates collectionPath.contains(value) into an Ops.IN operation, which LdapSerializer did not handle.

This PR adds Ops.IN handling for both shapes Querydsl produces:

• collectionPath.contains(value) emitted as IN(element, path) maps to (attribute=value), since LDAP equality on a multi-valued attribute matches if any value is equal.
• path.in(a, b) emitted as IN(path, constantCollection) maps to (|(attribute=a)(attribute=b)).

path.in(singleValue) already worked because Querydsl rewrites it to eq; a test now pins that behavior.

Tests were written first and confirmed failing on unmodified main with the exact exception from the issue, then made green by the change. The new tests reuse the existing QPerson / UnitTestPerson fixtures (the description attribute is already multi-valued). Full test suite passes: 86 tests, 0 failures.

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