fix ilk debt ceiling global sync and skip drip on onboarding

[mooncitydev]

hey team, moondev here. was poking at spell helpers and landed two fixes tied to open issues #69 and #70.

first, setIlkDebtCeiling could set an ilk line without touching global Line. that bites when you zero out an ilk dc but global stays inflated, or when you want one call to keep them aligned. added an optional _global flag that bumps global by the delta (same idea as increase/decrease ilk helpers). addNewCollateral now uses that instead of separate increase + set calls.

second, addNewCollateral was calling setIlkStabilityFee with drip enabled right after jug.init. nothing to accrue yet, just extra gas and a pointless drip on a fresh ilk. flipped that to false.

added tests for the global sync path and zeroing an ilk line. forge build is clean on my side; fork tests still want ETH_RPC_URL for mainnet.

closes #69
closes #70

[DaiFoundation-DevOps]

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