THRIFT-5979: Add native method types to PHP Server and Factory classes

[sveneld]

Migrates the public methods on lib/php/lib/Server/ and lib/php/lib/Factory/ from PHPDoc @param/@return annotations to native parameter and return types, plus closes a long-standing factory gap that surfaced during cross-test debugging.

The Server abstractions and the protocol/transport factories are isolated subtrees — they reference TTransport/TProtocol only via composition, so adding native types here does not cascade out to the Transport or Protocol hierarchies (separate sub-tickets).

Server

• TServer::serve() / stop() typed void.
• TSimpleServer / TForkingServer match the new abstract signatures, and drop the now-dead if ($transport != null) guards after accept(), which is non-nullable.
• TForkingServer's protected helpers (handleParent, handleChild, collectChildren) typed.
• TServerTransport::listen() / close() / acceptImpl() / accept() typed; accept() now returns TTransport (it was already that semantically — it throws on null), acceptImpl() returns ?TTransport, the null check switched to strict ===.
• TServerSocket overrides typed; acceptImpl() returns ?TSocket.
• TSSLServerSocket::listen() typed; acceptImpl() returns ?TSSLSocket.

Factory

• TProtocolFactory interface typed: getProtocol(TTransport): TProtocol.
• TBinaryProtocolFactory / TCompactProtocolFactory / TJSONProtocolFactory match with covariant concrete return types.
• TTransportFactoryInterface typed: getTransport(TTransport): TTransport.
• TTransportFactory / TFramedTransportFactory match with covariant return types where appropriate.
• New TBinaryProtocolAcceleratedFactory closes the long-standing gap where TBinaryProtocolAccelerated had no library-provided factory — the cross-test harness had to hand-roll one in test/php/TestServer.php. The ad-hoc class is dropped in favor of the library one. The new factory defaults strictWrite=true to match the protocol's own constructor default, distinguishing it from TBinaryProtocolFactory.

Test fixtures (latent issues surfaced by typed signatures)

• ServerStub::serve/stop now typed void.
• ServerTransportStub uses constructor property promotion with ?TTransport and matches abstract acceptImpl(): ?TTransport.
• TSimpleServerTest had stubs of the wrong class for the factories (TServerTransport where TTransport/TProtocol was expected); fixed.
• TForkingServerTest mocks had accept() returning null to simulate "no connection", which violated the now-typed TTransport return. Replaced with throwing TTransportException, which is what real accept() does on null and what the serve() loop already catches.
• TBinaryProtocolAcceleratedFactoryTest covers the new factory (7 tests).

Part of THRIFT-5960 — modernizing PHP runtime library typing. Builds on the property typing (THRIFT-5976), constructor promotion (THRIFT-5977), and declare(strict_types=1) (THRIFT-5978).

• Did you create an Apache Jira ticket? — THRIFT-5979
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"? — yes
• Did you squash your changes to a single commit? — yes
• Did you do your best to avoid breaking changes? — yes; signatures are typed exactly where Server/Factory subtrees terminate, no public-API removal, covariant return narrowings only. The new TBinaryProtocolAcceleratedFactory is purely additive.
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources. — N/A (code change)

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