[keelerm84]

TestDataV2 stored a flag builder under the key that the caller passed
to flag. use_preconfigured_flag discards the builder under the String
key from the flag data, so it missed a builder that flag(:key) created.
A later flag(:key) then returned the old builder, and update replaced
the preconfigured flag with it.

flag and FlagBuilderV2 now convert the key to a String. A Symbol key
and a String key get the same builder, and a built flag has a String
key, as a flag from LaunchDarkly has.

---

Note

Overview
TestDataV2 now normalizes flag keys to strings in flag and in FlagBuilderV2#initialize, so a Symbol and String key refer to the same cached builder and stored flags always use a string key (matching LaunchDarkly).

This fixes a test-data bug where building a flag with flag(:key) left a builder under the symbol key while use_preconfigured_flag only cleared the string-keyed entry—later flag(:key) could resurrect the old builder and overwrite the preconfigured flag on update.

Specs cover symbol/string equivalence, correct storage after updates, and a fresh default builder after preconfigured replacement when the flag was originally built with a symbol key.

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