Make the new-format templater output set granularity-invariant

[nick-gorman]

Two related but separable changes to the new-format templater. The first is the substance of the PR; the second would be better separated but I think the commits are entangled so I'm just leaving combined (sorry).

1. Granularity-invariant output set

Previously the new-format templater produced a different set of tables depending on regional granularity: the custom-constraint tables were written only at sub_regions, since coarser granularities collapse the flow paths they reference. That forced create_ispypsa_inputs to track a granularity-dependent output list and left downstream consumers checking for tables that may or may not exist.

This makes the output set identical at every granularity. Where there's nothing to constrain, the custom-constraint tables are output header-only ("all columns, no rows") rather than omitted, so the column shape is invariant and only the row contents differ.

2. Wire timeslices templating in

timeslices.py and its tests were already on main but nothing called it. This adds the call in create_ispypsa_inputs_template — _template_timeslices(load_timeslice_calendar(version), manual_tables["reference_year_sequence"]) — and registers timeslices in the output list. Templater tests patch load_timeslice_calendar with a two-window stub calendar; the CLI test pins the decoded row count against the shipped 7.5 calendar (content is covered by test_timeslices.py::test_shipped_calendar_decodes).

src/ispypsa/templater/
├── create_template.py                  → header-only cc tables at coarse granularity;
│                                          wire in timeslices
└── custom_constraints_from_plexos.py   → empty_custom_constraint_tables() + shared column constants
tests/
├── test_cli/test_create_ispypsa_inputs_new_table_formats.py  → verify against list_templater_output_files;
│                                                                 timeslices row-count pin
└── test_templater/test_create_ispypsa_inputs_template.py     → set-equality + header-only checks;
                                                                 timeslice stubs

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/ispypsa/templater/create_template.py	93.02% <100.00%> (ø)
...spypsa/templater/custom_constraints_from_plexos.py	100.00% <100.00%> (ø)

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[EllieKallmier]

Yep all makes sense to me, no notes :)