fix(circle): claim_streak_bonus and claim_referral_bonus now transfer…

[prettyjune04-ops]

… tokens

Both functions computed bonus amounts and emitted events but never performed any on-chain token transfer (issue #103).

Changes:

• Add CircleError::TokenNotSet = 38 to types.rs
• Add use soroban_sdk::token; import to contract.rs
• claim_referral_bonus: after computing bonus_total, load DataKey::Token and call token::Client::transfer(contract → referrer, bonus_total)
• claim_streak_bonus: after computing bonus_div, load DataKey::Token and call token::Client::transfer(contract → member, bonus_div)
• Both functions return TokenNotSet if set_token has not been called

Tests:

• test_claim_referral_bonus_transfers_tokens: verifies referrer balance increases by the exact calculated bonus amount
• test_claim_referral_bonus_no_double_claim: second claim errors
• test_claim_referral_bonus_no_token_set_returns_error: TokenNotSet path
• test_claim_referral_bonus_not_active_circle: rejects non-Active circle
• test_claim_streak_bonus_transfers_tokens: verifies member balance increases by the exact calculated streak bonus
• test_claim_streak_bonus_below_threshold_fails: streak < 3 errors
• test_claim_streak_bonus_no_token_set_returns_error: TokenNotSet path
• test_claim_streak_bonus_not_active_circle: rejects non-Active circle

Also fixed pre-existing issues blocking compilation:

• common/vrf.rs: soroban_sdk::Set does not exist in SDK v26; replaced with Vec for the used-positions tracking
• test.rs: add BytesN + Ledger testutils imports, use BytesN::from_array, switch to register_stellar_asset_contract_v2 + StellarAssetClient::mint

closes #103