[FEATURE] "portable" implementation for POSIX's uint64_t time.

[cederom]

Is your feature request related to a problem? Please describe.

• We are moving to POSIX compliant time representation (The Open Group Base Specifications Issue 8 IEEE Std 1003.1-2024 [1][2][3]) with uint64_t.
• POSIX sys/types.h [3] defines:

  time_t as "Used for time in seconds"
  time_t shall be an integer type with a width (see <stdint.h>) of at least 64 bits.

• What it solves:
  • year 2038 problem.
  • 32-bit system clock wrapped in ~497 days and almost every active board already enabled it.
  • runtime time overflow calculation errors after some weeks.
• What it breaks:
  • 8/16/32-bit platforms are most likely impacted by increased code size (i.e. ~2KB) when long long type is not natively supported.
  • time calculation will be slower on older platforms.
  • non-atomic time access (needs some additional protection).

This is a long standing challenge discussed on our mailing list [4][5].

Related PR: #18840, #14460, apache/nuttx-apps#3468.

[1] https://pubs.opengroup.org/onlinepubs/9799919799/
[2] https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/time.h.html
[3] https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/sys_types.h.html
[4] https://www.mail-archive.com/dev@nuttx.apache.org/msg12060.html
[5] https://www.mail-archive.com/dev@nuttx.apache.org/msg14534.html

Describe the solution you'd like

1. We are moving towards POSIX standard compliant time representation with int64_t type as default.
2. We need alternative portable implementation of the time representation on platforms that do not support native int64_t type that will solve size increase, slow down, and non-atomic time access protections, but still assure POSIX compliant interface.
3. Form the OS perspective both implementations should provide exactly the same and one-to-one compatible / replaceable solution, but the "portable" should assure best fit for the small architectures.

Describe alternatives you've considered

No response

Verification

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