fix: Check the deleted marker before decoding items from a persistent store

[kinyoklion]

Summary

FeatureRequesterBase decoded store items into the FeatureFlag/Segment model before checking whether the item was a deleted-item tombstone. The model decoder reads key, on, salt, fallthrough, and other properties from the raw array with no defaults, under strict_types=1. A tombstone that does not carry the full schema therefore threw a TypeError during decode. TypeError is an \Error, so it escaped the catch (\Exception) guard in LDClient and surfaced as an uncaught fatal in the application.

Minimal tombstones are a realistic input: several other server SDKs write {"version":N,"deleted":true} (with no key, and none of the other properties) to shared persistent stores when a flag or segment is deleted. With such a tombstone in the store:

• allFlagsState() fataled if the tombstone existed anywhere in the environment, even when the application never referenced the deleted flag.
• variation()/variationDetail() fataled when evaluating the deleted flag's key.

This change checks the deleted marker on the raw JSON array in getFeature, getSegment, and getAllFeatures before invoking the model decoder. Tombstones of any shape now behave as they should: the flag reads as not found and allFlagsState() skips it. Behavior for full-schema tombstones is unchanged, including the warning log on access.

Verified against a real Redis store via the predis integration: with {"version":9,"deleted":true} stored alongside live flags, allFlagsState() and evaluation of the deleted key both fataled before this change and now succeed, with the deleted key evaluating to the default value with a FLAG_NOT_FOUND reason.

SDK-2943

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Note

Overview
Stops decoding store items into FeatureFlag/Segment before noticing they are tombstones. Incomplete {"version":N,"deleted":true} records from other SDKs previously caused a TypeError (uncaught by LDClient) on variation() and allFlagsState().

getFeature, getSegment, and getAllFeatures now inspect deleted on the raw JSON and treat those items as not found (with the existing warning on single-item access). Full-schema tombstones behave the same. Tests cover live items plus full and minimal tombstones.

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[jsonbailey]

Minor nit on the comments.