Return Dmod_Pid_t from Dmod_Spawn/Dmod_RunDetached, add Dmod_GetProcessResult

[Copilot]

Process spawning functions returned int (exit code), conflating process identity with process result. Separated concerns: return PID from spawn, query result separately.

API Changes

• New type: Dmod_Pid_t (int32_t) represents process IDs. Positive = PID, negative = error code.
• Return type change: Dmod_Spawn() and Dmod_RunDetached() now return Dmod_Pid_t instead of int
• New API: Dmod_GetProcessResult(Dmod_Pid_t) retrieves exit status for a given PID

Implementation

• Weak implementations return DMOD_CURRENT_PROCESS_PID (1) when falling back to in-process execution
• Dmod_GetProcessResult() stub returns success for placeholder PID, error otherwise
• Real implementations (dmosi layer) will spawn actual processes and track results

// Before
int result = Dmod_Spawn(context, argc, argv);
// result was exit code, no way to track spawned process

// After
Dmod_Pid_t pid = Dmod_Spawn(context, argc, argv);
if (pid > 0) {
    int result = Dmod_GetProcessResult(pid);  // Query result separately
}

Callers in Dmod_SpawnModule() and Dmod_RunModuleDetached() cast back to int for compatibility, but now return PIDs as documented.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Dmod_Spawn i Dmod_RunDetached powinny zwracać Dmod_Pid_t</issue_title>
<issue_description>Aktualnie zwracają int jako result, a powinny zwracać Dmod_Pid_t (process ID). Dodaj też SAL API do odczytywania result na podstawie PID</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Dmod_Spawn i Dmod_RunDetached powinny zwracać Dmod_Pid_t #213

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