test-transaction-safety: perform the test on a filelog This test previously checked the transaction safety of splitting the changelog. The changelog is a special case, with delayed/diverted writes and we will stop inlining it soon. So we keep testing that transaction is safe around inline on another revlog type : a filelog. Minor comestic adjustement will be done in the next changesets.

test: clarify test-parseindex offsets We will make this revlog non-inline, so we clarify the code to make sure it is simple to adjust the test later.

test: use more globing for perf timing Not sure why we kept the number here.