fix(electron-sdk): localstorage indexing

[joker23]

This PR will fix the localstorage indexing by removing the previous nested structure:

ldcache-{credential}

To:

ldcache

The new structure is more consistent with other SDKs by calculating the storage index purely out of the context canonical keys.

This PR will also serialize the write to this cache so that multiple instances of this SDK could exist.

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Note

Medium Risk
Changes how cached flag/context data is persisted (single shared ldcache file and new async flush behavior), which can affect multi-client behavior and durability on disk-write failures.

Overview
Storage/indexing behavior changes. ElectronStorage no longer namespaces cache files by credential; it now always uses a single ldcache file under Electron userData and is exposed via a singleton getElectronStorage() used by ElectronPlatform/ElectronClient.

Write/flush semantics updated. set/clear now update the in-memory cache immediately and enqueue an async flush to disk (logging Error flushing storage to disk on failure), rather than only mutating cache after a successful write.

Tests/contract tests adjusted. Adds maxCachedContexts coverage (eviction and disabled caching when 0), updates ElectronStorage tests for new file path and flush behavior, and resets the storage singleton between contract-test clients via internal resetElectronStorage (also removing the contract-test singleton capability flag).

^{Reviewed by Cursor Bugbot for commit f084d37. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25661 bytes
Compressed size limit: 29000
Uncompressed size: 126143 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 179348 bytes
Compressed size limit: 200000
Uncompressed size: 830127 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31736 bytes
Compressed size limit: 34000
Uncompressed size: 112937 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 37181 bytes
Compressed size limit: 38000
Uncompressed size: 204409 bytes

[joker23]

@cursor review

[joker23]

@cursor review

[joker23]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.