fix: use the tightest bound in gtr and ltr when a range has redundant bounds

[Prafyl]

Fixes #904

outside() was taking the comparators with the highest and lowest versions as the edges of each set, which breaks when a set has more than one bound on the same side, like >1.0.0 >=2.0.0 <3.0.0 where it used >1.0.0 as the lower edge.

semver.gtr('1.5.0', '>1.0.0 >=2.0.0 <3.0.0') // was true, now false
semver.ltr('1.2.10', '1.2 <1.2.9 || >2.0.0')  // was true, now false

Now it picks the edges by operator instead, the tightest >/>= bound on one side and the tightest </<= on the other, and when two bounds are at the same version it takes the exclusive one. Doing it this way also shows when a set cant match anything, like >=2.0.0 <1.0.0, so a set like that is skipped instead of deciding the result for the whole range. That fixes gtr('3.0.0', '>=2.0.0 <1.0.0 || 1.x') which returned false. If every set is like that it still returns false like before.

Prerelease handling is the same as before, gtr('0.7.2-beta', '0.7.x') is still true.

i checked it against a brute force answer on about 97k random version/range pairs without prereleases, 7.8.5 got 13k of them wrong and this gets none. Added fixtures for both directions, the >/>= tie, and sets that cant match anything. Tests pass with coverage still at 100% and lint is clean.