phase1-01: Implementation of StateVector and ReactorConfig

[anibalrojosan]

Issue: phase1-01: Implementation of StateVector and ReactorConfig
Branch: feat/core-data-structures
Type: backend
Priority: High
Dependencies: phase1-00

Description

Define the base structures for the simulator. Following a TDD-like approach, unit tests must be developed alongside the implementation to ensure data integrity.

Mathematical Context

• Reference: See @docs/MATH_MODEL.md#state-variables.
• Core Logic: Define the 17 state variables ($C_i$) with their respective units ($gCOD \cdot m^{-3}$, $gN \cdot m^{-3}$, etc.).
• Reactor Geometry: Implement volume ($V$) and surface area ($A$) calculations based on depth ($h$).

Tasks

• Test: Write unit tests for StateVector (validation of 17 variables and units).
• Code: Implement src/core/state.py to satisfy tests.
• Test: Write unit tests for ReactorConfig (geometry calculations).
• Code: Implement src/core/reactor.py and config/reactor_setup.yaml.
• Run quality checks: uv run ruff check src/core/
• Format code: uv run ruff format src/core/

Acceptance Criteria

• All new unit tests pass in local and CI environments.
• StateVector allows access by name (e.g., state.S_NH4) and index.
• Minimum 90% code coverage for the new modules.
• Code passes Ruff validation.