Update unreleased changes

[prckent]

Proposed changes

Update the changelog with the major unreleased changes since the last release. "Minor" PRs have been removed to keep the list short while still e.g listing most of the bug fixes. Changes were approximately grouped and sorted by hand.

Initial list built via variants of

gh search prs --merged-at 2025-01-01..2025-01-31 -R QMCPACK/qmcpack \
    --json title,url,repository,number -L 1000 \
    --jq '.[]|("* " + .title + " [#" + (.number|tostring) +"]("+ .url + ")\n")' 

What type(s) of changes does this code introduce?

• Documentation or build script changes

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• NA. Code added or changed in the PR has been clang-formatted
• NA. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• NA. Documentation has been added (if appropriate)

[prckent]

Test this please