Adding strahlenschutzverordnung waste limits

[shimwell]

Summary

• Add German Strahlenschutzverordnung (StrlSchV) 2018 Anlage 4 clearance limits as predefined options for Material.waste_disposal_rating()
• Support 8 clearance pathways covering unrestricted release, landfill disposal, incineration, metal recycling, soil, and building rubble
• Clearance values are compared in Bq/g units (German convention), extending the existing Ci/m³ support for NRC/Fetter limits

Details

The German radiation protection regulation (StrlSchV 2018, Anlage 4, Tabelle 1) defines nuclide-specific clearance values for releasing radioactive materials from regulatory control. A material passes clearance when the sum-of-fractions (activity/limit for each nuclide) is ≤ 1.0 — the same methodology already used by waste_disposal_rating() for NRC and Fetter limits.

This PR adds 8 predefined limit sets, each corresponding to a column in Anlage 4:

Limit name	Pathway	Column
StrlSchV_unrestricted	Unrestricted clearance of solid/liquid substances	3
StrlSchV_metal_recycling	Metal scrap recycling	14
StrlSchV_landfill_100	Landfill disposal, facility receiving ≤100 Mg/a	8
StrlSchV_landfill_1000	Landfill disposal, facility receiving ≤1000 Mg/a	10
StrlSchV_incineration_100	Incineration, facility receiving ≤100 Mg/a	9
StrlSchV_incineration_1000	Incineration, facility receiving ≤1000 Mg/a	11
StrlSchV_soil	Soil surface clearance	7
StrlSchV_rubble	Building rubble clearance (>1000 Mg/a)	6

Usage:

rating = mat.waste_disposal_rating(limits='StrlSchV_unrestricted')
breakdown = mat.waste_disposal_rating(limits='StrlSchV_metal_recycling', by_nuclide=True)

parse_strlschv.zip

The clearance values were extracted from the official German legal database (https://www.gesetze-im-internet.de/strlschv_2018/anlage_4.html). A parser script
(parse_strlschv.py) is attached to this PR for reproducibility and future updates to the regulation.

Note on + (daughter equilibrium) entries: Some nuclides in Anlage 4 are listed with a + suffix (e.g., Cs-137+), indicating that the clearance value accounts for short-lived daughter nuclides in secular equilibrium. Of the 91 +-only parents in the table, 47 have daughters that also appear as independent entries, which could lead to some degree of double-counting in the sum-of-fractions calculation. The daughter limits tend to be much less restrictive than the parent + limits, so their individual contributions to the sum are minor. A follow-up PR will address this by using the depletion chain file to identify and exclude daughter nuclides already covered by a parent's + clearance value. I want to add support for this but I don't want to make this PR to big, so I offer to follow this PR on this. I would also be happy to follow up this PR with a PR that moves Fetter and StrlSchV data to a datafile perhaps in the data folder.

Fixes # (issue)

Checklist

• I have performed a self-review of my own code
  - [ ] I have run clang-format (version 18) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)