Support recurring vote-streak rewards and migrate legacy streak config/state

[BenCodez]

Motivation

• Add support for recurring vote-streak rewards (reward every N completions) in addition to one-time rewards at N.
• Smooth upgrade path for users upgrading from older plugin versions by migrating legacy per-user streak fields and the deprecated VoteStreak config section into the new VoteStreaks format.

Description

• Added a recurring boolean to VoteStreakDefinition and updated its constructor and usages to carry the new option.
• Updated reward logic in VoteStreakHandler.processVoteForDefinition to honor recurring (reward every N completions when true, otherwise reward only once at N).
• Implemented legacy migration helpers getLegacyStreakProgress and migrateLegacyProgressIfNeeded to import old per-user streak counters into the new serialized streak state on first use.
• Added legacy config loader methods loadLegacy and loadLegacyType to ingest the deprecated VoteStreak -> Day|Week|Month sections, create VoteStreakDefinition entries, and disable the old config nodes; also added Recurring support to the example SpecialRewards.yml.

Testing

• Ran the unit tests in VoteStreakHandlerTest, including configLoader_loadsDefinition_andGetDefinitionWorks, processVote_whenAlreadyCountedThisPeriod_doesNotIncrementStreakAgain, processVote_acceptsOldFiveFieldFormat_andUpgradesState, processVote_migratesLegacyProgressIntoNewState, and configLoader_migratesLegacyVoteStreakSection.
• All unit tests passed (no failing assertions).

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Codex Task