Add prototype paramdb api

[awarde96]

Add prototype paramdb api that allows conversion of ECMWF shortname to param id and vice versa using either the paramdb directly or a local copy.

Adds a ParamDB class to pymetkit.py for resolving ECMWF parameter metadata (shortname ↔ longname ↔ param ID, units) with both online (live API) and offline (bundled YAML) modes.

New files

• parameter_metadata.yaml — bundled offline parameter data generated from the parameter-database
• generate_parameter_metadata.py — standalone script to regenerate the YAML from the ECMWF API (python -m pymetkit.generate_parameter_metadata)

Changes

• pymetkit.py — adds ParamDB class; imports yaml, requests, Path
  *. __init__.py — explicitly exports ParamDB
• pyproject.toml — adds pyyaml + requests to dependencies; includes parameter_metadata.yaml in package data

Usage

from pymetkit import ParamDB

# Offline (default, uses bundled YAML)
db = ParamDB()
db.shortname_to_longname("2t")        # "2 metre temperature"
db.param_id_to_shortname(129)         # "z"
db.longname_to_param_id("Geopotential")  # 129
db.get_units("tp")                    # "m"
db.get_metadata(167)                  # full dict

# Online (fetches from codes.ecmwf.int)
db = ParamDB(mode="online")

Lookup via get_metadata / get_units accepts param ID (int), shortname, or longname interchangeably.

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.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.33%. Comparing base (fa88f33) to head (c2b7ee8).

Additional details and impacted files

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  Files          303      303           
  Lines        11601    11601           
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  Hits          7232     7232           
  Misses        4369     4369           

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