fix(scale): avoid duplicate final tick with bounds:'data' and fractional max

[contactjawad]

What

A linear scale using bounds: 'data' emits a duplicate final tick (and a duplicate axis label) when the data maximum has a fractional part that rounds down to the last generated integer tick. For example, data [0, 5.4] produces labels ['0','1','2','3','4','5','5'].

Why

In generateTicks, with bounds: 'data' the niceMax is the raw data max, and numSpaces is Math.ceil((niceMax - niceMin) / spacing). The loop therefore emits ticks up to and including the integer just below the data max (e.g. 5 for a max of 5.4). niceMax is then rounded to the tick factor and unconditionally pushed again:

} else if (!maxDefined || niceMax === max) {
  ticks.push({value: niceMax});
}

When the rounded niceMax equals the last loop-emitted tick, that value is added twice.

How

Guard the final push so it does not duplicate the last emitted tick:

} else if (!maxDefined || niceMax === max) {
  if (!ticks.length || ticks[ticks.length - 1].value !== niceMax) {
    ticks.push({value: niceMax});
  }
}

Test

Added a spec in test/specs/scale.linear.tests.js alongside the existing "Should bound to data" test, using dataset [0, 5.4], bounds: 'data' and ticks.autoSkip: false, asserting the labels are ['0','1','2','3','4','5']. Before the fix the labels are ['0','1','2','3','4','5','5'], so the test fails on the previous behavior and passes with the fix.