Pin new dependency versions and regenerate with xmsconan 2.16.0

[wdolinar]

Regenerates CI files with xmsconan 2.16.0 (was 2.15.2) and repoints xms_dependencies at the versions released during this rollout.

Dependency pins

	was	now
xmscore	7.0.8	7.0.11
xmsgrid	9.0.9	9.0.10
xmsinterp	7.0.8	7.0.9
xmsextractor	10.0.6	10.0.7

The older versions are unusable for two independent reasons: xmsconan 2.15.3 pinned conan~=2.31.0, which changes package_id so builds detach from binaries published under an unpinned conan; and xmsconan 2.15.1 moved testing_sources out of the published library, so libraries built between then and 2.16.0 do not export the testing helpers this repo links. The versions pinned here are built under both the conan pin and xmsconan 2.16.0.

CI changes

• Flake job renders .flake8 via xmsconan_gen and runs plain flake8 _package.
• Build/deploy steps pin xmsconan==2.16.0 and conan~=2.31.0.
• actions/checkout@v2 → @v4 (v2 is deprecated).

Base branch

This targets worktree-xmsconan-migration, not master — master has no build.toml, so the xmsconan migration lives on that branch and this stacks on top of it. Merging this does not land anything on master.

Verification

All 18 GitHub Actions checks pass, including both macOS jobs.

The two continuous-integration/appveyor/* checks fail. That is pre-existing and unrelated: appveyor already fails on the base branch, there is no appveyor.yml in the repo (it is a stale external integration from the 2019 era), and this branch touches only XmsGridtrace-CI.yaml and build.toml.

To be released as 2.0.3.