fix(round): round negative Fractions half away from zero

[yu2971512385-ui]

round resolves a tie differently depending on the type of the value:

math.round(-2.5)                     // -3
math.round(math.bignumber(-2.5))     // -3
math.round(math.fraction(-2.5))      // -2   <-

math.round(-0.25, 1)                 // -0.3
math.round(math.bignumber(-0.25), 1) // -0.3
math.round(math.fraction(-0.25), 1)  // -0.2 <-

number and BigNumber round a half away from zero (roundNumber, and decimal.js's default ROUND_HALF_UP which rounds away from zero). Fraction.round follows Math.round instead, which rounds a half towards positive infinity, so every exact half with a negative fraction lands on the other side. Positive values agree across all three types, which is why this is easy to miss.

floor, ceil and fix are already consistent across the three types; round is the one that is not.

Change

roundFraction rounds the magnitude and re-applies the sign, and the three Fraction signatures use it. Positive fractions are untouched, and the existing behaviour for number, bigint, BigNumber, Unit and matrices is unchanged.

Tests

A new case in test/unit-tests/function/arithmetic/round.test.js covers -1/2, -3/2, -5/2, -2/3, -1/3, and -1/4 with 1 decimal (as number and as BigNumber), and asserts the same expectations against the number and BigNumber implementations so the three stay pinned together. The new test fails before the change; npx mocha test/unit-tests --recursive passes after it (6653 passing), and eslint is clean.

Note on Complex

Complex.round has the same tie behaviour (math.round(math.complex(-2.5, -2.5)) → -2 - 2i), since complex.js also uses Math.round. Fixing that means rounding the parts in mathjs rather than delegating, which changes more than this fix — happy to follow up with a separate PR if you would like that made consistent too.