ci: build through job-script recipes; hpc lane is hpc-atos

[mcocdawc]

Description

Draft until ecmwf/ci-infrastructure#97 is on main; this uses its run-job-script action.

• The runner build is .ci/build.sh.j2, rendered and run by run-job-script; .github/actions/build-eckit goes.
• The recipe is the plain runner template; ctest-args now feeds its test block.
• execution = "hpc-atos"; the HPC recipe extends cmake-atos.sh.j2 (its new name). Workflows regenerated: -hpc → -hpc-atos.

Reproduce a leg locally: ci-infrastructure-render --list, then ci-infrastructure-render --leg '<job title>' -o ci-job.sh.

🤖 Generated with Claude Code

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌦️ >> Documentation << 🌦️
https://sites.ecmwf.int/docs/dev-section/eckit/pull-requests/PR-365

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.70%. Comparing base (a578f84) to head (0399eb8).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #365      +/-   ##
===========================================
- Coverage    68.74%   68.70%   -0.05%     
===========================================
  Files         1188     1188              
  Lines        63017    63017              
  Branches      4743     4743              
===========================================
- Hits         43320    43293      -27     
- Misses       19697    19724      +27     

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