Add Print/PrintLine overloads for SystemTime

[its-mohitkumar-7]

Summary

Adds Print(value: SystemTime) / PrintLine(value: SystemTime) to
Print.rux.

Problem

UtcTime() / LocalTime() return SystemTime, but Print/PrintLine
had no overload for it:

error: no matching overload for 'Print' with argument types (SystemTime)

Fix

• Added the two overloads to Src/Print.rux, plus
  import Std::Time::SystemTime;.
• Added flat (non-nested) helpers PadTime2/PadTime3 for zero-padding —
  nested functions currently fail on the ELF linker.
• Output format: YYYY-M-DD HH:MM:SS.mmm.

Scope

Only tested on Linux. SystemTime is a different type per target, so
I can't say if this works on Windows/macOS/BSD without checking there too.

Testing

Manually verified on Linux against all Std::Time functions via both
Print and PrintLine. LocalTime() output matches UtcTime(), as
expected since it currently just forwards to it on Linux.