Auto-create raw_data_location in dynamic_data_compiler and static_table

[nick-gorman]

Summary

cache_compiler already creates the cache directory if it doesn't yet exist; the other two entry points raised UserInputError. Same parameter on three sibling APIs behaving differently is real API friction — every new user has to mkdir separately before their first dynamic_data_compiler call, and the inconsistency is unexplained.

This PR lifts cache_compiler's pattern (including the better "exists as a file, not a directory" error wording it already had) into a shared _validate_raw_data_location helper called from all three entry points.

Behaviour now consistent across dynamic_data_compiler, cache_compiler, and static_table:

raw_data_location value	Result
None	UserInputError("...is None")
path exists as a file	UserInputError("...exists as a file, not a directory")
path doesn't exist	os.makedirs(path)
path exists as a directory	no-op

Why

• First-run UX. New users shouldn't need a mkdir step before their first NEMOSIS call.
• API consistency. Same kwarg name on three sibling functions should mean the same thing.
• Error-quality net positive. dynamic_data_compiler and static_table previously gave a worse error when the path was a file (collapsed into "does not exist"); the shared helper fixes that.
• Closes the release-notes overclaim — the "raw_data_cache is auto-created" bullet was previously only true for cache_compiler.

Trade-off considered: typo silence

Auto-create means a typo like nem_cahce silently creates a new empty dir at the typo location rather than raising — the user wonders why their first download is slow. The countervailing cost is forcing every user to mkdir once. Typos are rare and trivially recoverable (re-run with the correct path); the mkdir tax hits every new install. The trade-off favours auto-create, and that's already the established behaviour in cache_compiler.

Tests

• Drop the two *_missing_includes_path_in_error tests on dynamic/static (asserted the now-obsolete raise-on-missing behaviour).
• Add *_is_a_file and *_missing_is_auto_created for all three entry points (6 new tests; cache_compiler now has explicit coverage of the file-vs-dir distinction it already implemented).

Test plan

• uv run pytest tests/ — 439 passed, 1 skipped (was 433 + 1 on master pre-change; net +6 from the new tests).

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