Add .mailmap to consolidate contributor identities

[francisco-dlp]

The problem

GitHub attributes commits to accounts via registered email addresses. Several contributors committed under multiple addresses or display names (university-era addresses, login-as-name), which fragments git shortlog/git blame and, where the address is not linked to a GitHub account, hides commits from the contributors view. For example Tomas Ostasevicius's Cambridge-era address (to266@cam.ac.uk) carries 155 exspy commits that GitHub attributes to nobody.

The fix

A .mailmap consolidating every duplicate or broken identity found in the git history (verified against git log and checked with git check-mailmap). The same consolidation was proposed for hyperspy/hyperspy in gh-3685; the canonical name and email per person match that mailmap for cross-repo consistency.

Verification

git shortlog -sne after the mailmap (selection): Francisco de la Peña 1496 (was split across 4 identities), Eric Prestat 1103, Jonas Lähnemann 326 (was 2), Tomas Ostasevicius 254 (was 2: 99 + 155), Michael Sarahan 148 (was 4, incl. a broken unknown <Mike@.(none)> and @superstem.org), Magnus Nord (was 6 identities incl. ntnu/glasgow/jobbPC), Vidar Tonaas Fauske 137 (was 2), Alberto Eljarrat (was 2), Carter Francis (was 4, incl. commits as shaw), Petras Jokubauskas (was 3), Tom Furnival (was 3), Tom Slater (was 2), Timothy Poon (was 4), Thomas Aarholt (was 2), Zezhong Zhang (was 2), Giulio Guzzinati (was 2), Francisco de la Peña (was 5 incl. Francisco@ogre.msm.cam.ac.uk... the Cambridge ogre machine). Unique author identities: 91 -> 62.

Notes

• Metadata-only change: no code, no packaging.
• Authored with AI assistance per the dev guide policy (Assisted-by: OmO:Kimi-K3 in the commit trailer).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.33%. Comparing base (10e53fa) to head (17f9900).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #183   +/-   ##
=======================================
  Coverage   88.33%   88.33%           
=======================================
  Files         100      100           
  Lines        7764     7764           
  Branches      932      932           
=======================================
  Hits         6858     6858           
  Misses        632      632           
  Partials      274      274           

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[francisco-dlp]

CI note for reviewers: the diff is .mailmap + a towncrier fragment only, so the two failures are not caused by this change. Build / Check links fails on external link drift (same class as the link-check failures seen across the ecosystem this week). ubuntu-py3.13-dev needs a look: recently merged PRs (#174, #171) pass all their test jobs, so this may be a newly-introduced upstream environment issue rather than drift on my side - my branch is based on current upstream main, so the job runs the same config as main's next PR will. The mailmap is verified with git check-mailmap and git shortlog (identity count 91 -> 62).