fix: use correct shard index when creating encoder

[adklempner]

Problem

When library consumer specifies a cluster ID and shard index when creating an encoder, it means they are using static sharding and explicitly specifying which shard index (and thus pubsub topic) should be used.

Currently, when an encoder is created this way, it uses the autosharding algorithm to determine the shard index based on content topic, which can lead to unexpected results if it doesn't match the shard index specified by the consumer.

Solution

• Make shard property optional in SingleShardInfo.
• Fix conditional that evaluates to falsy when shard is set to 0 (this was preventing static sharding from being used)

Notes

• Resolves #1874

[github-actions[bot]]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
Waku node	180.73 KB (-0.07% 🔽)	3.7 s (-0.07% 🔽)	2.7 s (+8.76% 🔺)	6.4 s
Waku Simple Light Node	180.86 KB (-0.07% 🔽)	3.7 s (-0.07% 🔽)	2.1 s (+2.04% 🔺)	5.7 s
ECIES encryption	23.11 KB (-0.02% 🔽)	463 ms (-0.02% 🔽)	538 ms (-16.89% 🔽)	1000 ms
Symmetric encryption	22.59 KB (+0.05% 🔺)	452 ms (+0.05% 🔺)	789 ms (+56.95% 🔺)	1.3 s
DNS discovery	72.42 KB (0%)	1.5 s (0%)	1.8 s (+19.54% 🔺)	3.2 s
Peer Exchange discovery	73.96 KB (0%)	1.5 s (0%)	929 ms (+22.21% 🔺)	2.5 s
Local Peer Cache Discovery	67.64 KB (0%)	1.4 s (0%)	1.5 s (+82.95% 🔺)	2.9 s
Privacy preserving protocols	38.87 KB (0%)	778 ms (0%)	1.1 s (+0.17% 🔺)	1.8 s
Waku Filter	111.25 KB (-0.17% 🔽)	2.3 s (-0.17% 🔽)	1.5 s (-11.53% 🔽)	3.7 s
Waku LightPush	110.23 KB (0%)	2.3 s (0%)	1.3 s (-11.78% 🔽)	3.5 s
History retrieval protocols	110.71 KB (0%)	2.3 s (0%)	2 s (+53.11% 🔺)	4.2 s
Deterministic Message Hashing	4.83 KB (0%)	97 ms (0%)	40 ms (-61.62% 🔽)	137 ms

[adklempner]

@danisharora099 The reason I made the shard field optional is because right now there's no other way for createEncoder to differentiate between static sharding and autosharding. e.g. in the test { clusterId: 0 } makes the function determine shard index using the content topic, but {clusterId: 0, shard: 1} will always use shard index 1, no matter the content topic.