Make robustspecies wordsize-agnostic (fix 32-bit Modeling CI on master)

[ChrisRackauckas-Claude]

Note: This PR should be ignored until reviewed by @ChrisRackauckas.

What changed and why

robustspecies (src/network_analysis.jl:1402) built its result as Int64[] and then stored it in NetworkProperties.robustspecies, which is declared Vector{Int} (src/reactionsystem.jl:121). On 32-bit Julia Int == Int32, so the assignment throws TypeError: in setfield!, expected Vector{Int32}, got a value of type Vector{Int64}. This is the same class of bug as #1552; it has been latent since 8b26cb794 ("implement robustness for deficiency one", 2024-06) and only surfaced once the 32-bit Modeling CI lane was added in #1550. The fix is a one-token change, Int64[] -> Int[].

Failing master CI job (commit 7e42f3e): https://github.com/SciML/Catalyst.jl/actions/runs/34655420896/job/103454181607

Verification

The existing test/network_analysis/crn_theory.jl tests are the discriminating regression test: they error on unmodified master with 32-bit Julia and pass with the fix. Run locally with julia +1.12~x86 (juliaup, 1.12.7+0.x86.linux.gnu) and julia +1.12 (1.12.7+0.x64.linux.gnu) via a script that includes the test file inside a @testset.

Before the fix, 32-bit Julia 1.12.7 (unmodified master 7e42f3e):

Julia 1.12.7, 32-bit, Int = Int32
CRN Theory: Error During Test at .../test/network_analysis/crn_theory.jl:101
  Test threw exception
  Expression: Catalyst.robustspecies(IDHKP_IDH) == [2]
  TypeError: in setfield!, expected Vector{Int32}, got a value of type Vector{Int64}
  Stacktrace:
   [1] setproperty!(nps::Catalyst.NetworkProperties{Int32, ...}, sym::Symbol, x::Vector{Int64})
     @ Catalyst .../src/reactionsystem.jl:137
   [2] robustspecies(rn::ReactionSystem{Catalyst.NetworkProperties{Int32, ...}})
     @ Catalyst .../src/network_analysis.jl:1417
CRN Theory: Error During Test at .../test/network_analysis/crn_theory.jl:114
  Test threw exception
  Expression: Catalyst.robustspecies(EnvZ_OmpR) == [6]
  TypeError: in setfield!, expected Vector{Int32}, got a value of type Vector{Int64}
Test Summary: | Pass  Error  Total     Time
CRN Theory    |   66      2     68  1m08.8s

After the fix, 32-bit Julia 1.12.7:

Julia 1.12.7, 32-bit, Int = Int32
Test Summary: | Pass  Total     Time
CRN Theory    |   68     68  1m34.3s

After the fix, 64-bit Julia 1.12.7 (also 68/68 before the fix, i.e. no behaviour change on 64-bit):

Julia 1.12.7, 64-bit, Int = Int64
Test Summary: | Pass  Total     Time
CRN Theory    |   68     68  1m18.7s

typos over the diff and over src/network_analysis.jl: clean. Runic.main(["--check", "--diff", "src/network_analysis.jl"]): exit 0, no diff.

Not verified

• Only test/network_analysis/crn_theory.jl was run locally, not the full Modeling group or the other test groups (the change is a single literal inside robustspecies, which no other file references besides this test and the docs).
• Docs build not run (no docstring or public API change).
• src/ still contains other explicit Int64 uses (e.g. chemistry_functionality.jl:291, dsl.jl:577, and throughout spatial_reaction_systems/); I did not audit whether any of those are assigned into Int-typed fields. This PR deliberately fixes only the one that fails on master CI.

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