S12.17: Tunable TCP connect and TLS handshake timeouts

[DavidCozens]

Parent epic: #31 (E12: Error Handling)
Follow-on from: #276 (S12.14 — fail-fast streams + eager Service drain)

Background

Two timeouts are currently hardcoded by S12.14:

• TCP connect — 200 ms
  (Platform/Windows/Source/SolidSyslogWinsockTcpStream.c:88-101,
  Platform/Posix/Source/SolidSyslogPosixTcpStream.c:24).
• TLS handshake — 5 s
  (HANDSHAKE_TIMEOUT_MS in Platform/OpenSsl/Source/SolidSyslogTlsStream.c).

Both values were tuned for the BlockStore drain-rate scenario on
loopback / LAN, which is the right default for the BDD suite. They are
too tight for real WAN deployments — e.g. a far cloud SIEM behind a
high-RTT link or a transparent proxy, where 200 ms connect and 5 s
handshake routinely exceed the budget even when the path is healthy.

Tradeoff to surface

• Tight bounds keep the BlockStore discard policy responsive during
  outages — overflow is observable in tests within seconds.
• Loose bounds match real WAN deployments but slow the drop-detection
  path during a true outage; overflow scenarios take proportionally
  longer to trigger.

This story does not change the defaults — it only makes them tunable
per deployment.

Scope

Two design options to choose between in implementation:

A. Compile-time CMake variables. SOLIDSYSLOG_TCP_CONNECT_TIMEOUT_MS
and SOLIDSYSLOG_TLS_HANDSHAKE_TIMEOUT_MS, plumbed via
add_compile_definitions. Cheapest; integrators rebuild to change.

B. Config-injected fields. Add connectTimeoutMs to
SolidSyslogStreamSenderConfig and handshakeTimeoutMs to
SolidSyslogTlsStreamConfig. Zero / unset means "use the existing
default constant". Higher cost; integrators set per-deployment without
rebuilding.

Recommend B — config injection is the pattern the rest of the
library has been moving toward (see CLAUDE.md "Callback Conventions");
compile-time variables would be a step backwards. Confirm before
implementation.

Verification

• Unit: assert the configured values reach the bounded select()
  loop in PosixTcpStream / WinsockTcpStream and the bounded
  handshake retry loop in TlsStream. Existing fakes
  (SocketFake, WinsockFake, plus the OpenSSL test seam) capture the
  deadline argument.
• No BDD changes — the BDD harness keeps the current default; tunable
  values are a deployment-time concern, not a behavioural one for the
  suite.

Out of scope

• Read / Send timeouts during normal operation — unrelated; not part
  of fail-fast contract.
• Adaptive / exponential backoff between reconnect attempts — separate
  story if needed.

Acceptance

• Defaults unchanged (BDD suite still passes with no config change).
• Setting non-zero connectTimeoutMs / handshakeTimeoutMs is
  observed in the bounded-wait paths in unit tests.
• Coverage stays at 100% line/branch.