feat(espcoredump): Include boot time and unix time in header (IDFGH-12792)

[nebkat]

Unfinished and untested but creating draft to gather feedback. Will create corresponding patch for esp-coredump python.

Core dumps do not contain any form of timestamp to help identify when a crash occurred.

This patch adds two new fields to the core dump header - boot time and unix time:

• Boot time (microseconds since boot) is useful in determining whether a crash occurred immediately after boot or many hours in, which can aid in debugging. Observing the core dump data can indirectly provide this information but requires additional steps. In applications with known bugs (e.g. memory leaks) knowing this in advance can save time by reducing unnecessary debugging.
• Unix time (microseconds since epoch) may provide hints as to why the crash occurred in applications that depend on external inputs, and is useful when organizing files, both on local and remote storage. In my application we copy core dumps to an SD card, but we have no way of knowing whether a particular core dump occurred 1 week or 1 year ago.

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[igrr]

Thanks for the nice improvement idea @nebkat, I left some comments...

cc @erhankur