Implement a few gas optimizations (#246)

* perf: use a bitmap instead of storage mapping for storing claimed epochs
feat: replace "claimedEpochs" storage var with a view function implementation

* perf: batch token transfers and state updates in "claimMany" function
refactor: remove superfluous assignment of uint256 to 0 in "claimMany" function
docs: add TODO in "claimMany" function

* fix: bug in "claimEpoch" function

* refactor: use "claimedEpochs" function call instead of "_claimedEpochsBitMap" storage mapping
refactor: rename "claimedEpochs" function to "claimedEpoch"
docs: remove TODO at "claimMany" function
test: rename "testClaimMultipleClaims" test function to "testClaimFourIndividualClaims"
test: rename "testClaimMany" test function to "testClaimManyOnce"

* feat: change state mutability of "_claimedEpochsBitMap" from "private" to "internal"

* test: add Foundry unit test for "claimedEpoch" function
test: add balance assertions for "testClaimManyOnce" test
chore: re-generate gas snapshot

* chore: re-generate gas snapshot