implement spearbit suggested optimizations

[jrhea]

resolves #476

• reduce the number of div operations by 2 when calculating fees in openLong()

resolves #478

• optimize return statements in _applyCheckpoint()

resolves #482

• in query(), deltaSum.divDown(deltaTime * 1e18) = deltaSum * 1e18 / (deltaTime * 1e18) computation is the same as deltaSum / deltaTime.
• in calculateAPRFromReserves(), To scale to one year,do mulDivDown(365 days, _positionDuration). Currently, annualizedTime is first computed as an 1e18-based percentage value
• in calculateInitialBondReserves, FixedPointMath.ONE_18.mulDown(_timeStretch) is just _timeStretch.

[coveralls]

coverage: 95.894% (-0.01%) from 95.904% when pulling 4a4a647 on optimizations into 662cc79 on main.

[github-actions]

Hyperdrive Gas Benchmark

Benchmark suite	Current: 4a4a647	Previous: 662cc79	Deviation	Status
addLiquidity: min	763 gas	763 gas	0%	🟰
addLiquidity: avg	45185 gas	45342 gas	-0.3463%	✅
addLiquidity: max	80502 gas	80652 gas	-0.1860%	✅
checkpoint: min	514 gas	514 gas	0%	🟰
checkpoint: avg	29398 gas	29513 gas	-0.3897%	✅
checkpoint: max	82905 gas	83031 gas	-0.1518%	✅
closeLong: min	852 gas	852 gas	0%	🟰
closeLong: avg	21528 gas	21621 gas	-0.4301%	✅
closeLong: max	87459 gas	87560 gas	-0.1153%	✅
closeShort: min	854 gas	854 gas	0%	🟰
closeShort: avg	22398 gas	22480 gas	-0.3648%	✅
closeShort: max	87717 gas	87914 gas	-0.2241%	✅
initialize: min	803 gas	803 gas	0%	🟰
initialize: avg	159484 gas	159736 gas	-0.1578%	✅
initialize: max	233224 gas	233501 gas	-0.1186%	✅
openLong: min	740 gas	740 gas	0%	🟰
openLong: avg	40795 gas	41238 gas	-1.0743%	✅
openLong: max	223505 gas	224074 gas	-0.2539%	✅
openShort: min	760 gas	760 gas	0%	🟰
openShort: avg	47627 gas	47676 gas	-0.1028%	✅
openShort: max	217404 gas	217530 gas	-0.0579%	✅
removeLiquidity: min	740 gas	740 gas	0%	🟰
removeLiquidity: avg	62278 gas	62451 gas	-0.2770%	✅
removeLiquidity: max	122657 gas	122749 gas	-0.0749%	✅

This comment was automatically generated by workflow using github-action-benchmark.

[jalextowle]

LGTM. Nice work!