Update GMAO site configs and util/gmao scripts

[mathomp4]

Description

GMAO site configurations and util/gmao batch install scripts.

• Site configs and READMEs for discover, discover-gmao, nas, nas-toss5, bucy (new, tier 2) and macos.gmao (clang/Flang 23.1.2, gcc 15.3.0/16.2.0, NAG).
• util/gmao/batch_install.sh: --datestamp, --suffix, opt-in --with-ai, macOS Flang support and 256-character install padding for macOS build caches; plus README and monitor_install.py updates.
• Ignore util/gmao/** in the three build workflows, like configs/sites/**.
• Require nccmp 1.11.0.0 on the GMAO sites, which GEOS needs. Use +trust_ecbuild_flags for ectrans, oops and ioda with %oneapi on discover and NAS.
• Remove util/gmao/patch_ecbuild_ectrans.py, superseded by +trust_ecbuild_flags.

Only configs/sites/*, util/gmao/* and .github/workflows are changed.

Dependencies

• waiting on Add trust_ecbuild_flags variant to ioda and oops #2167 (trust_ecbuild_flags variant for ioda and oops; the discover and NAS site files request it)
• waiting on Update ecbuild to 3.15.2, allow fms 2026.01.01 and nccmp 1.11.0.0 #2165 (allows nccmp 1.11.0.0 in configs/common/packages.yaml; the site require blocks conflict with the current @1.9.0.1 pin until then)
• a follow-up GMAO PR adds the geos-dev-flang template that batch_install.sh selects for macOS clang (other batch_install.sh uses are unaffected)

Issues addressed

Related to #2157, #2159.

Applications affected

None. All changes are site-specific or in GMAO scripts.

Systems affected

GMAO discover, discover-gmao, NAS, NAS toss5, bucy and macOS (macos.gmao).

Testing

• CI: the build workflows are skipped for this PR (configs/sites/** and util/gmao/** are ignored, and the commit has [skip ci]).
  • GitHub actions CI tests pass
  • GitHub actions CI tests do not pass (provide explanation)
  • GitHub actions CI tests skipped (site and script changes only)
• Additional testing:
  • GMAO stacks built on discover and bucy from the combined branch (including Update ecbuild to 3.15.2, allow fms 2026.01.01 and nccmp 1.11.0.0 #2165 and Add trust_ecbuild_flags variant to ioda and oops #2167 changes).
  • macOS builds with GCC and clang/Flang.

Checklist

• This PR addresses one issue/problem/enhancement or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.
• All necessary updates to the documentation (spack-stack wiki) will be made when this PR is merged

[mathomp4]

Whoops. Opened as draft. Undrafted!

[climbfuji]

The oneapi-ifx failure is known (#2171), the other tests make no sense, since this PR doesn't modify any of the files used in CI (CI workflow script update to skip GMAO-only changes are good - the CI runs kicked off).