fix: Distributed value removed while fail-safe active

[nikcio]

Fixes #553

Implements a check before removing distributed values from the cache to skip removal when the options are using failsafe to allow a factory failure to use the stale value.

More information is noted on the issue. Let me know if this approach is appropriate to fix the issue 😄

[Copilot]

Pull request overview

This pull request fixes an issue where distributed cache values were being removed even when fail-safe was active. The fix adds a check in the DistributedExpireEntry methods (both sync and async versions) to skip the distributed cache removal operation when fail-safe is enabled, allowing stale values to remain available for use during factory failures.

Key Changes:

• Modified DistributedExpireEntry in FusionCache_Sync.cs to return early with success when fail-safe is enabled
• Modified DistributedExpireEntryAsync in FusionCache_Async.cs with the same fail-safe check
• Backplane notification still occurs to inform other cache instances of the expiration event

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/ZiggyCreatures.FusionCache/FusionCache_Sync.cs	Added fail-safe check to skip distributed cache removal during entry expiration
src/ZiggyCreatures.FusionCache/FusionCache_Async.cs	Added fail-safe check to skip distributed cache removal during entry expiration (async version)

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