Fixes for ERA6 re-encoding

[dsarmany]

Description

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.

[Copilot]

Pull request overview

Adjusts mars2grib concept matchers to better align ERA6 re-encoding behavior with expected tables/level/point-in-time handling for specific parameter IDs.

Changes:

• Remove the chemical-products special-case that selected TablesType::Custom in the tables matcher.
• Expand/shift several parameter ranges in the point-in-time matcher (incl. additional 21x/262xxx codes).
• Update level matching for SFC/O2D to align with the updated parameter coverage (incl. 262900, 262906, 262907, and updated 21x ranges).

Impacted files under src/metkit/mars2grib/**:

• src/metkit/mars2grib/backend/concepts/tables/tablesMatcher.h
• src/metkit/mars2grib/backend/concepts/point-in-time/pointInTimeMatcher.h
• src/metkit/mars2grib/backend/concepts/level/levelMatcher.h

Documentation status (src/metkit/mars2grib/docs/**): ✅ in sync (no public-behavior documentation found that enumerates/depends on these specific param-ID lists).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/metkit/mars2grib/backend/concepts/tables/tablesMatcher.h	Stops selecting custom tables for chemical params (now always default).
src/metkit/mars2grib/backend/concepts/point-in-time/pointInTimeMatcher.h	Adjusts param inclusion ranges (notably 21x and 262xxx additions/expansions).
src/metkit/mars2grib/backend/concepts/level/levelMatcher.h	Aligns SFC and O2D level matching with updated param ranges/new ocean-related params.

[Copilot]

tablesMatcher() now always returns TablesType::Default, but it still reads param via get_or_throw and keeps matchAny/range using-declarations and the param-matcher include. This adds an unnecessary dictionary access (and can throw if param is absent) despite param no longer influencing the result. Consider removing the param lookup and the now-unused matchAny/range aliases/includes, or otherwise documenting/justifying why param is still required here.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 62.00%. Comparing base (8bdc834) to head (34dbdd1).
⚠️ Report is 3 commits behind head on release/1.18.0.

Files with missing lines	Patch %	Lines
...it/mars2grib/backend/concepts/level/levelMatcher.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release/1.18.0     #194   +/-   ##
===============================================
  Coverage           61.99%   62.00%           
===============================================
  Files                 303      303           
  Lines               11663    11661    -2     
  Branches             1048     1049    +1     
===============================================
- Hits                 7231     7230    -1     
+ Misses               4432     4431    -1     

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