Preserve first error's diagnostic code in op->naTime during parallel solve

[Copilot]

In parallel mode, op->naTime was unconditionally overwritten on every NA error via #pragma omp atomic write, making the diagnostic code (used to generate the final error message in rxode2_df.cpp) non-deterministic — it would reflect whichever thread wrote last, not the first error encountered.

Changes

• inst/include/rxode2parseGetTime.h — getLag, getRate, getDur, handleInfusionItem: replace unconditional atomic write of op->naTime with a read-check-write pattern
• inst/include/rxode2parseHandleEvid.h — getAmt: same fix

op->badSolve remains an unconditional atomic write (any thread setting it to 1 is correct).

Before

int newNaTime = 1 + 10*cmt;
#pragma omp atomic write
op->naTime = newNaTime;  // overwrites every time — last writer wins

After

int curNaTime;
#pragma omp atomic read
curNaTime = op->naTime;
if (curNaTime == 0) {
  int newNaTime = 1 + 10*cmt;
#pragma omp atomic write
  op->naTime = newNaTime;  // only set if not yet recorded
}

This restores the intent of the original if (op->naTime == 0) guard while keeping writes thread-safe.

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