Move TCPSession lifetime to shared_ptr ownership, fix the whole double-delete/UAF class of crash

Every crash root-caused earlier tonight (Subscription::subscribers,
TCPServer::sessions, the Socket::write()/eventReceived() re-arm race) was
the same underlying shape: some thread calling a method - or Thread::run()
calling delete - on a TCPSession* while another thread concurrently freed
that same object, because nothing actually guaranteed the object stayed
alive for the duration of a call. Mutex-based patches at each individual
call site kept narrowing the window without closing it (confirmed live,
repeatedly, via AddressSanitizer under concurrent load - each fix produced
a new, different crash signature at the same underlying race), and adding
more locks around every write() call also works against the fifo-based
design's own goal: no thread should have to block just to hand a message
to another thread's session.

TCPSession now derives from std::enable_shared_from_this<TCPSession> and
exposes pin() - a safe upgrade from a stored raw pointer to a real,
ownership-extending shared_ptr, returning nullptr instead of throwing once
the object's real owner has let go. TCPServer::sessions is now the one
real strong-owning shared_ptr<TCPSession> per live session; every other
place that stores a TCPSession* (Subscription::subscribers, Zephora's own
sessionsByPlayerName, GroupObject's membership list, etc.) is just a
non-owning observer and must pin() before touching the object.

A second, distinct problem: Thread::run()'s epoll dispatch starts from a
raw void* of unknown validity. An early version of this fix used
dynamic_cast<TCPSession*> to identify session objects before calling
pin() - confirmed live via AddressSanitizer that dynamic_cast itself
segfaults on a stale pointer, since it has to read the (potentially freed)
object's own vtable to work at all. TCPSession::tryGet()/TCPServer::
isKnownListeningSocket() replace that: both look the raw pointer up as a
key in a registry, never dereferencing it for the check itself - safe to
call on any value, live session, immortal listening socket, or fully
freed garbage alike.

Verified via an AddressSanitizer-instrumented build under sustained
concurrent load (up to 15-way parallel connect/subscribe/create/disconnect
cycles, multiple rounds, 100+ total connections) with zero errors, then
against the real production build with a genuine 500-connection load test
(463/500 succeeded; the rest hit the process's own file-descriptor
ulimit under peak burst, an unrelated and separately deferred tuning
matter, not a crash).

Files touched: TCPSession.h (enable_shared_from_this, pin(), the tryGet()
registry), TCPServer.h/.cpp (sessions as shared_ptr, isKnownListening
Socket() registry, lock made protected for subclasses), Thread.cpp (the
whole dispatch rewrite), Subscription.cpp/SubscriptionManager.cpp (every
subscriber write() site now pin()s first), ConsoleServer.cpp (logSend()
was iterating `sessions` with no lock at all - fixed alongside the type
change it needed anyway).

Socket.h

@@ -124,6 +124,23 @@ namespace core {
 
     protected:
 
+      // Set by Timer's own constructor (see its own doc comment) - a
+      // Timer is always a Socket subobject privately/multiply inherited
+      // alongside a session's own real network Socket (e.g. ZephoraSession
+      // : TCPSession, Timer), never a standalone connection with its own
+      // independent lifetime. eventReceived()'s ordinary keepAlive
+      // contract - returning false means "delete me" (see Thread::run(),
+      // which then does exactly that on this object's own Socket* base) -
+      // is correct for a real connection but catastrophic here: deleting
+      // through a pointer to just the Timer subobject deletes the entire
+      // composite object at the WRONG size (Timer/Socket's own smaller
+      // size, not the true derived object's), a new-delete-type-mismatch
+      // confirmed live via AddressSanitizer under concurrent load. A
+      // Timer's own fd is already correctly torn down as part of its
+      // containing object's own destructor chain; it never needs (and
+      // must never trigger) independent deletion through this path.
+      bool preventSelfDelete = false;
+
       EPoll &ePoll;           // The EPoll control object.
 
       void setBufferSize(int length);