Release 10.1.0: date the changelogs for the v10.1.0 tag #328

Change

Step 3 of #301: the last PR against release/10.x before the tag.

1. Set all five ## [10.1.0] headings to the tag date, 2026-10-19, in the commit that gets tagged (CONTRIBUTING.md, "Changelog").
2. Reword the RangeSet.Contains line in the root and EF changelogs, and the EF NodaTime package's note. They name EF Core 10.0.15 as though it were out. [release/10.0] Fix Contains handling for read-only collections dotnet/efcore#39114 sits on efcore's closed 10.0.15 milestone, but the newest EF Core 10 on NuGet is 10.0.13, so the lines should say that the patch is planned and wasn't published when 10.1.0 shipped. This came out of the 10.1.0 review on 2026-10-19. The stopgap switch name, Microsoft.EntityFrameworkCore.Issue37081, was checked against the efcore diff.

Then tag v10.1.0 on the merge commit.

Before this step, the whole candidate (3ed738e) was run on the .NET 11.0.0-rc.2 runtime by roll-forward, at the floor and on EF Core 10.0.13 / Npgsql EF 10.0.3, and every suite passed (#324 has the table).

Done when

The PR is merged into release/10.x with ChangelogConventionTests passing, and its merge commit is the one tagged v10.1.0.