fix: space Verso docstring closers in Section 1.2.2

[Chessing234]

Summary

• Insert the missing space before -/ on Exercise 1.2.12(i)/(ii) and 1.2.22(i)/(ii) Verso docs (same class of issue as fix: insert missing space before Verso docstring closers #600 / fix: space Verso docstring closers; correct BddAbove/Below comments #615).
• Leaves the relabelled 1.2.22(ii') line alone — already spaced on main via Measure theory 1.2.2: Exercises 1.2.18 and 1.2.22 have two parts, not three #632.

Test plan

• CI build green

[teorth]

This now needs a small rebase: #632 merged and relabelled the third 1.2.22 docstring from (iii) to (ii'), so the Exercise 1.2.22(iii) (Product measure formula)-/ line this PR targets no longer exists.

The merged version already carries the closer space on that one line, so the resolution is just to drop that hunk. The other four lines here — 1.2.12(i), 1.2.12(ii), 1.2.22(i), 1.2.22(ii) — are untouched by #632 and still wanted.

Context on the relabel: Exercise 1.2.22 has only two parts in the text, with part (ii) reading "show that E × F is Lebesgue measurable, with m(E × F) = m(E) m(F)" — so the two theorems LebesgueMeasurable.prod and Lebesgue_measure.prod are the two halves of (ii). Same situation for Exercise 1.2.18.

[Chessing234]

rebased onto main and dropped the 1.2.22(iii)/(ii') hunk — the other four closers are still spaced.

[Chessing234]

@teorth ready for another look when you have a minute — tip is rebased and the four closer spaces are still there.