S24.22: FreeRtosSysUpTime does not account for FreeRTOS tick-counter wrap #609

Parent epic: #254

Surfaced by CodeRabbit during the S23.09 platform-header docs (PR #607):
#607 (comment)
(re-raised: #607 (comment))

The gap

SolidSyslogFreeRtosSysUpTime_Get is
(uint64) xTaskGetTickCount() * 100 / configTICK_RATE_HZ cast to uint32.
xTaskGetTickCount() is the raw FreeRTOS tick counter, which wraps at its own
width (2^32 ticks ~= 49.7 days at 1 kHz; far sooner under
configUSE_16_BIT_TICKS). At that wrap the reported uptime jumps backwards and
resets well before the RFC 3418 modulo-2^32 hundredths period.

Only the FreeRtos implementation is affected: Posix (CLOCK_BOOTTIME) and Windows
(GetTickCount64) are real since-boot counters whose RFC 3418 claims are accurate.

Options (to decide here)

• Compile-time guard (preferred / David's instinct). A #error /
  _Static_assert that fails the build when the tick width cannot back a faithful
  32-bit TimeTicks (e.g. configUSE_16_BIT_TICKS, or a tick rate that makes the
  scaled wrap period too short), with a comment telling the integrator how to
  become compliant (use a 32-bit TickType_t, or opt into the extension below).
  Refuses to silently ship a subtly-wrong uptime; the integrator makes an
  informed choice.
• Overflow extension. Track tick overflows (a wrap counter maintained against
  a stored last-tick) to extend the base to a monotonic 64-bit tick count before
  scaling — then the uint32 result wraps correctly per TimeTicks on every
  config.
• Accept + document. Ship as-is with the limitation documented (current
  interim state).

Amend the doc when fixed

The SolidSyslogFreeRtosSysUpTime_Get doc-comment was softened in PR #607 to
"...not a full TimeTicks counter" as an interim. When the fix lands (guard
and/or extension), update that comment to state the new contract — e.g. "RFC 3418
compliant; a #error guards unsupported tick configs."

Done when

• Either uptime is monotonic to the full RFC 3418 range (extension) or an
  unsupported tick config fails to compile (guard), and the
  SolidSyslogFreeRtosSysUpTime_Get doc-comment is updated to match.