fix simtime update in write_FM and write_SM functions

[Sahil-u07]

While porting behavior from Python to C++, I found that [write_FM] and [write_SM] were writing timestamps into the output but never advancing the [simtime] member. That left simulations stuck at the same time across steps.

This change makes the C++ functions increment [simtime] by [delta] immediately after a successful write (vector payloads only, matching the Python implementation).

[Copilot]

Pull request overview

This pull request fixes a critical bug where the C++ write_FM and write_SM functions were writing timestamps into output files but failing to advance the simtime member variable, causing simulations to be stuck at the same time across steps. The fix adds simtime += delta statements immediately after successful writes in both functions, matching the behavior of the Python reference implementation.

Changes:

• Added simtime += delta to write_FM function for vector payloads after successful file write
• Added simtime += delta to write_SM function for vector payloads after successful shared memory write

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