Handle underflow condition of network out slot stats metric

[hpatro]

Fixes test failure (https://github.com/valkey-io/valkey/actions/runs/10146979329/job/28056316421?pr=837) on 32 bit system for slot stats metric underflow on the following condition:

server.cluster->slot_stats[c->slot].network_bytes_out += (len * listLength(server.replicas));

• Here listLength accesses len which is of unsigned long type and multiplied with len (which could be negative). This is a risky operation and behaves differently based on the architecture.

clusterSlotStatsAddNetworkBytesOutForReplication(-sdslen(selectcmd->ptr));

• sdslen method returns size_t. applying - operation to decrement network bytes out is also incorrect.

This change adds assertion on len being negative and handles the wrapping of overall value.

Scenario:

Test code:

#include<stdio.h>
#include<stdint.h>

int main(int argc, char argv[]) {
	uint64_t test = 0;
	unsigned long len = 1;
	test += 23;
	test += (-23 * len);
	printf("%llu", test);
	return 0;
}

64 bit build

$ gcc test.c
test.c: In function ‘main’:
test.c:9:20: warning: format ‘%llu’ expects argument of type ‘long long unsigned int’, but argument 2 has type ‘uint64_t’ {aka ‘long unsigned int’} [-Wformat=]
    9 |         printf("%llu", test);
      |                 ~~~^   ~~~~
      |                    |   |
      |                    |   uint64_t {aka long unsigned int}
      |                    long long unsigned int
      |                 %lu
$ ./a.out
0

32 bit build:

$ gcc -m32 test.c
$ ./a.out
4294967296

[hpatro]

Related #720

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.41%. Comparing base (b4d96ca) to head (029f320).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #840      +/-   ##
============================================
+ Coverage     70.38%   70.41%   +0.02%     
============================================
  Files           112      112              
  Lines         61462    61467       +5     
============================================
+ Hits          43261    43280      +19     
+ Misses        18201    18187      -14     

Files	Coverage Δ
src/cluster_slot_stats.c	94.01% <100.00%> (+0.18%)	⬆️
src/replication.c	87.30% <100.00%> (+0.13%)	⬆️

... and 10 files with indirect coverage changes