Hooking up electricity buy price and more correctly

[johnjasa]

Connect buy_price from technology cost models to the SLC controller

Resolves the linked issue. There were some complexities because of the flexibility afforded by grid electricity price inputs (can be a scalar, plant_life, or an 8760) as well as the feedstocks setup.

1. Wired each cost-aware system-level controller's {tech_name}_buy_price input directly to the corresponding technology's own buy-price input via an OpenMDAO 3.44 input-to-input connection in H2IntegrateModel.add_system_level_controller, so a single prob.set_val() on (for example) plant.grid.electricity_buy_price now propagates to the SLC instead of silently using only the YAML default.
2. The connection is created on self.model (not self.plant), because OpenMDAO 3.44 only resolves input-to-input connections registered on the top-level group; using promoted names works because the plant subgroup is added with promotes=["*"].
3. Added a small _get_tech_buy_price_input_name helper in system_level_control_base.py (shared by both files) that returns the tech's actual input name (electricity_buy_price for Grid, price for Feedstock).
4. Added _get_buy_price_default_and_shape so the SLC's {tech}_buy_price input is created with the same shape as the tech's input (driven by buy_price_mode for Grid; by price-array length for Feedstock). This is required because input-to-input connections need matching shapes; per-timestep, per-year, constant, and scalar configurations are all handled.
5. Updated _buy_price_marginal_cost to broadcast scalar / per-year arrays up to n_timesteps so the existing merit-order dispatch code is unchanged.
6. Fixed the test_slc_complex_profit_max test, which was implicitly relying on the bug (the example's grid_buy_price = sell_price + 0.02 makes grid never profitable, but the SLC was using the constant 0.06 default, which sometimes beat the sell-price spikes). The corrected assertion verifies grid is never dispatched, which is now the right behavior.

Section 1: Type of Contribution

• Feature Enhancement
  • Framework
  • New Model
  • Updated Model
  • Tools/Utilities
  • Other (please describe):
• Bug Fix
• Documentation Update
• CI Changes
• Other (please describe):

Section 2: Draft PR Checklist

• Open draft PR
• Describe the feature that will be added
• Fill out TODO list steps
• Describe requested feedback from reviewers on draft PR
• Complete Section 8: New Model Checklist (if applicable)

Type of Reviewer Feedback Requested (on Draft PR)

Implementation feedback:

• _get_tech_buy_price_input_name currently recognizes electricity_buy_price (Grid) and price (Feedstock). If other techs grow buy-price inputs, this is the spot to extend. It may be worthwhile to standardize the naming now or in the future?

Other feedback:

• N/A

Section 3: General PR Checklist

• PR description thoroughly describes the new feature, bug fix, etc.
• Added tests for new functionality or bug fixes
• Tests pass (If not, and this is expected, please elaborate in the Section 6: Test Results)
• Documentation
  • Docstrings are up-to-date
  • Related docs/ files are up-to-date, or added when necessary
  • Documentation has been rebuilt successfully
  • Examples have been updated (if applicable)
• CHANGELOG.md
  • At least one complete sentence has been provided to describe the changes made in this PR
  • After the above, a hyperlink has been provided to the PR using the following format:
    "A complete thought. PR XYZ", where
    XYZ should be replaced with the actual number.

Section 4: Related Issues

Fully resolves #790

Section 5: Impacted Areas of the Software

Section 5.1: New Files

• N/A

Section 5.2: Modified Files

• h2integrate/core/h2integrate_model.py adds the input-to-input connection for cost_per_tech: buy_price techs and updates the relevant docstring.
• h2integrate/control/control_strategies/system_level/system_level_control_base.py adds the two helpers, sizes the SLC {tech}_buy_price input to match the tech, and broadcasts in _buy_price_marginal_cost.
• h2integrate/control/control_strategies/system_level/test/test_slc_examples.py replaces the buggy "grid used when needed" assertion with the now-correct "grid not dispatched when always unprofitable" check.

Section 6: Additional Supporting Information

The user explicitly requested using the OpenMDAO 3.44 input-to-input connection feature here. The 25 unit tests in test_slc_controllers.py keep using set_val("slc.{tech}_buy_price", ...) because those tests instantiate the SLC component in isolation (no tech subgroup to connect from), so they validate the controller behavior independently of the new wiring.

Section 7: Test Results, if applicable

N/A

Section 8 (Optional): New Model Checklist

N/A