feat: send over TCP instead of UDP

[DavidCozens]

UDP to TCP, by putting a SolidSyslogStreamSender over an lwIP TCP stream. The network
retransmits rather than dropping, and a send fails when the collector is gone instead of succeeding
into a void. Records are framed by octet count per RFC 6587, which is what a receiver expects on a
stream transport.

struct SolidSyslogLwipRawTcpStreamConfig tcpConfig = {.Sleep = SyslogSleep};

struct SolidSyslogStreamSenderConfig senderConfig = {
    .Resolver = SolidSyslogLwipRawResolver_Create(),
    .Stream   = SolidSyslogLwipRawTcpStream_Create(&tcpConfig),
    .Address  = SolidSyslogLwipRawAddress_Create(),
    .Endpoint = CollectorEndpoint,
};
struct SolidSyslogSender* sender = SolidSyslogStreamSender_Create(&senderConfig);

Taken with the sequence number, this completes the loss story: the transport detects loss where it
happens, and the sequence reveals afterwards anything the transport could not. It is also what
makes the delivery-failed and delivery-restored events from the error-handler stage meaningful.

The store is still the Null object, so a record whose send fails is reported but not kept. The
device learns that delivery is failing without yet being able to do anything about it; retaining
the record is the store stage's job.

TCP before TLS is deliberate. It is the smaller step — a stream, a connect and a framing rule, with
no certificates in the picture — and it is what a later store-and-forward stage will spool onto.

The stream takes a Sleep callback because a connect is not instantaneous and the library will not
pick a blocking primitive on your behalf; one vTaskDelay is the whole of it.

When you need it. If the device must know that delivery is failing — to raise an alarm, to fall
back, to start storing. Over UDP it never finds out.

RFC 6587 is Historic, and the IESG recommends TLS over plain TCP for new deployments. Plain TCP
is here for collectors you do not control, and as the step a later storage stage will spool onto,
before cryptography arrives.

[DavidCozens]

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