feat(cluster): add a ProtocolVersion enum for withProtocolVersion()

[CodeLieutenant]

What this does

withProtocolVersion() took a bare int, so a caller had to know that the native protocol version is the byte the protocol itself defines, and a typo produced a runtime error instead of a type error.

Adds Cassandra\ProtocolVersion, an int-backed enum whose cases carry that byte, so V1 through V5 match CASS_PROTOCOL_VERSION_V1 through _V5.

$cluster = Cassandra::cluster()
    ->withProtocolVersion(Cassandra\ProtocolVersion::V4)
    ->build();

Why the int overload stays

The enum names only the five native protocol versions, but the driver also understands versions it does not name, such as the DSE ones. So the signature is ProtocolVersion|int and the int path keeps its own range check.

Input	Result
ProtocolVersion::V4	4
3	3, reported back as ProtocolVersion::V3
66	66, reported back as the plain int
0	InvalidArgumentException

Behaviour change worth noting

Cluster\Builder's protocolVersion property now reports the matching enum case when the value maps to one, and falls back to the plain int when it does not. Code that read that property as an int and used a named version will now see an enum. Reading ->value covers both.

Descriptor generator

The generator did not understand enums: it emitted a create_object handler and an object-allocating registration for every class it saw, which is wrong for an internal enum whose cases the engine builds and owns. It now recognises the enum kind and registers through zend_register_internal_enum() with no instance handlers.

This is the part most worth a careful read, since it changes code generation for every stub, not just this one.

Verification

• Build clean, clang-tidy 0 findings on Cluster/Builder.c.
• Unit suite 868 passed, 0 failures.
• Each row of the table above checked against a built extension.

Note on the branch

This branch previously carried #152, which is merged. Its three commits were dropped during a rebase onto trunk as already upstream, so this PR is the single new commit. The branch name is left over from that work and does not describe this change.

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