Add CHP merge order analysis for expansion project PRs

[Copilot]

Analyzed 6 CHP expansion PRs (#552-557) to determine optimal merge order that minimizes conflicts across 8-20 changed files per PR, with critical overlap in src/constraints/chp_constraints.jl and src/core/chp.jl.

Recommended Merge Order

Phase 1: Foundation

1. PR Multiple CHPs #553 - Multiple CHPs (FIRST)
   • Restructures single CHP → array of CHPs
   • Refactors 20 files to use p.s.chps[t] and p.chp_params[t] accessors
   • Establishes loop structure: for t in p.techs.chp
   • All other PRs depend on this architectural change

Phase 2: Core Features
2. PR #554 - CHP Independent Thermal - Adds independent thermal production constraints
3. PR #552 - Off-grid CHP - Adds operating reserve logic for off-grid scenarios

Phase 3: Operational Improvements
4. PR #555 - CHP Production Factor Input - Small field addition (3 files, 67 lines)
5. PR #556 - Avoid CHP Binaries - Conditional binary creation optimization
6. PR #557 - CHP Ramp Rate Limitation (LAST) - Adds ramp rate constraints

Critical Conflicts

src/constraints/chp_constraints.jl (modified by 4 PRs):

• PR Multiple CHPs #553 changes constraint structure from single CHP to loops
• PR CHP Independent Thermal #554 adds new constraint functions for independent thermal mode
• PR Avoid CHP Binaries When Not Needed #556 refactors function signatures to make binary creation conditional
• PR CHP Ramp Rate Limitation Option #557 adds ramp rate constraint function

src/core/chp.jl (modified by ALL 6 PRs):
Field additions combine cleanly in sequence:

Base.@kwdef mutable struct CHP <: AbstractCHP
    operating_reserve_required_fraction::Real = 0.0  # PR #552
    name::String = "CHP"  # PR #553
    can_produce_thermal_independently::Bool = false  # PR #554
    production_factor_series::Union{Nothing, Vector{<:Real}} = nothing  # PR #555
    ramp_rate_fraction_per_hour::Float64 = 1.0  # PR #557
end

Rationale

Merging PR #553 last would require rewriting all previously merged PRs to use the new multiple CHP structure. Merging it first requires updating other PRs once (p.s.chp → p.s.chps[1]), but establishes the foundation for all enhancements.

Timeline: ~1-2 weeks (one PR per day with validation buffer)

Original prompt

See CHP Expansion project which includes a collection of pull requests for REopt.jl. I'd like to figure out the best order of merging to create the least amount of conflicts.

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