Provide masked/unmasked meta for calls to 'as_lazy_data'

[pp-mo]

iris._lazy_data.as_lazy_data has changed : See iris#5801.

Current failing tests against iris latest,
e.g. see https://github.com/SciTools/iris-grib/actions/runs/8892392519/job/24416350591

[pp-mo]

NOTE: this is rather tiresome as, at present the new code only works with the new iris version.

Effectively, iris._lazy_data.as_lazy_data was not a private routine which we could freely change,
since iris-grib uses it !

So, before SciTools/iris#5801 it had no 'meta' keyword,
but now after that it requires one.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 63.33333% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 89.16%. Comparing base (fea1607) to head (29ae999).
Report is 3 commits behind head on main.

Files	Patch %	Lines
src/iris_grib/__init__.py	66.66%	6 Missing and 1 partial ⚠️
src/iris_grib/message.py	55.55%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #463      +/-   ##
==========================================
- Coverage   89.51%   89.16%   -0.35%     
==========================================
  Files           8        8              
  Lines        2450     2474      +24     
  Branches      416      418       +2     
==========================================
+ Hits         2193     2206      +13     
- Misses        161      170       +9     
- Partials       96       98       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.