Implement LRU eviction policy for the SDK in-memory cache

[Kingsman-99]

Overview

The current cache evicts entries only by TTL. Under high usage with many unique keys, the cache grows unbounded until TTL expires. Add LRU (Least Recently Used) eviction to cap memory usage.

Acceptance Criteria

• StellarSplitSDK({ cache: { maxEntries: 500 } }) config option
• When maxEntries is reached, the least recently accessed entry is evicted before adding a new one
• LRU order updated on every cache hit (read counts as access)
• sdk.getCacheStats() adds evictions: number to the existing stats
• LRU and TTL work together: an entry can be evicted by either mechanism
• maxEntries defaults to 1000 when cache is enabled; 0 means no LRU cap
• Implementation uses a Map + doubly-linked list for O(1) get/put
• Unit tests: fill cache to maxEntries + 1, verify oldest entry evicted; verify LRU order respected

[abikedaniel22]

@abikedaniel22 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer I'll like to work on this issue please can you assign me

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[Malcolm-Wander]

@Malcolm-Wander has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer,I’d love to work on this issue please…promise to do bad accurate and swift job,thank you.

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[Toyinoje]

@Toyinoje has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, i will like to work on this issue

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[wowamaxe-glitch]

@wowamaxe-glitch has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'm a full-stack developer and I'd like to take this issue.
I understand the requirements and will follow the existing project structure, keep the implementation clean, and include proper tests where applicable.

ETA: 1–3 days (depending on scope)

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Congratulations, @wowamaxe-glitch! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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