fix: add reentrancy guards and dust absorption to distribution (#85)

[Tranquil-Flow]

Summary

• Adds ReentrancyGuardUpgradeable to AbstractDistributionStrategy, BaseDistributionManager, and MultiStrategyDistributionManager
• Applies nonReentrant to claimAndDistribute() in both managers and distribute() in both strategies
• Fixes dust accumulation: last recipient/strategy absorbs rounding remainder (up to N-1 wei) instead of leaving tokens trapped in the contract
• Removes redundant require($.strategies.length > 0, ...) check (already enforced at initialization)
• Corrects NatSpec: "Dust from integer division is left in the contract" → accurate description of new dust-free behavior

Closes #85

Test plan

• Verify __ReentrancyGuard_init() called in all three initializers
• Verify nonReentrant on all claimAndDistribute() and distribute() functions
• Verify dust absorption: total amount distributed equals input amount (no wei left behind)
• EqualDistributionStrategy — last recipient gets remainder
• VotingDistributionStrategy — last recipient gets remainder
• MultiStrategyDistributionManager — last strategy gets remainder
• Full suite: 191 tests pass