Refactor counter wrap-around logic into helper function

[Copilot]

Addresses feedback from PR #902: duplicated wrap-around delta logic and platform-dependent counter width.

Changes

• Helper function: calculate_counter_delta(uint32_t current, uint32_t previous) - static inline, uses unsigned arithmetic's natural modular wrap-around
• Platform-independent: uint32_t instead of unsigned long ensures consistent 32-bit semantics regardless of platform word size
• Applied to 9 counters: BytesSent, BytesReceived, PacketsSent, PacketsReceived, ErrorsSent, RetransCount, FailedRetransCount, RetryCount, MultipleRetryCount
• Local scope: Variables declared within usage blocks

Implementation

static inline uint32_t calculate_counter_delta(uint32_t current, uint32_t previous)
{
    // Unsigned arithmetic naturally handles wrap-around correctly
    // Example: 0x00000001 - 0xFFFFFFFF = 2 (in uint32_t)
    return current - previous;
}

// Usage
uint32_t curr = sta[i].dev_stats.cli_BytesSent;
uint32_t prev = dev_stats_last->cli_BytesSent;
uint32_t diff = calculate_counter_delta(curr, prev);

Previous approach used explicit wrap-around calculation with ULONG_MAX, which is 64-bit on 64-bit platforms, causing incorrect delta computation when counters wrap at 32-bit boundary.

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