Add ExplicitImports QA checks via SciMLTesting run_qa

[ChrisRackauckas-Claude]

This PR should be ignored until reviewed by @ChrisRackauckas.

Summary

Wires ExplicitImports.jl into the QA group through SciMLTesting's run_qa (explicit_imports = true), running all six checks and making them pass:

• Standard: no_implicit_imports, no_stale_explicit_imports, all_explicit_imports_via_owners, all_qualified_accesses_via_owners
• Public-API: all_qualified_accesses_are_public, all_explicit_imports_are_public

Fixes (FIX > DECLARE-PUBLIC > minimal-IGNORE)

Implicit -> explicit imports (no_implicit_imports): the blanket using Graphs / using DataStructures / using DocStringExtensions / using PrecompileTools (and the SparseArrays extension's blanket usings) are now explicit using X: names. Names owned by Graphs.SimpleGraphs (SimpleDiGraph, SimpleEdge, add_edge!, add_vertex!, rem_edge!) are imported from that owner — which also makes the previously non-public Graphs.SimpleEdge qualified access a public explicit import.

Stale import (no_stale_explicit_imports): the DataStructures v0.18->v0.19 IntDisjointSets->IntDisjointSet rename used import ... IntDisjointSet plus const IntDisjointSet = IntDisjointSets, whose const shadowed the import so it read as stale. Both version branches now alias to a single internal _IntDisjointSet via using ... as, used at the one call site.

Non-public qualified accesses (all_qualified_accesses_are_public): fixed by rewriting where clean —

• Iterators.filter -> filtered generator (maximal_matching)
• Iterators.peel -> indexed loop (hypergraph)
• Base.Fix1(f, x) -> equivalent closures (hypergraph; Fix1 is non-public on the 1.10 LTS)

Ignored (minimal, documented, per-check)

Three remaining accesses are unavoidable, ignored via ei_kwargs on all_qualified_accesses_are_public:

• Base.OneTo — the vertex-range type returned by 𝑑vertices / condensation-graph vertices; public Base API as of Julia 1.11 but only retroactively marked, so flagged on the 1.10 LTS. Rewriting to UnitRange would change the return type.
• Base.print_matrix — the only routine for tabular Base.show of a matrix view.
• Base.typeinfo_implicit — the documented (internal) hook to suppress the element-type header when printing an array of HighlightInt.

Public API declared

None needed: BipartiteGraphs already exports its public names, and the two public-API checks (all_explicit_imports_are_public, all_qualified_accesses_are_public) concern what this package imports from its dependencies, not what it exports.

Test deps

Added ExplicitImports and bumped SciMLTesting to >= 1.4 (its run_qa gained the ExplicitImports option in 1.4.0) in both the main Project.toml and test/qa/Project.toml. JET handling is unchanged.

Verification (local)

Ran on Julia 1.10 (LTS) and Julia 1.11: all six ExplicitImports checks PASS on both.

QA group (GROUP=QA, Julia 1.11):

Test Summary:     | Pass  Total
Quality Assurance |   12     12      # Aqua + 6 ExplicitImports checks
ExplicitImports                     |    6      6
  no_implicit_imports               |    1      1
  no_stale_explicit_imports         |    1      1
  all_explicit_imports_via_owners   |    1      1
  all_qualified_accesses_via_owners |    1      1
  all_qualified_accesses_are_public |    1      1
  all_explicit_imports_are_public   |    1      1

The 2 pre-existing Aqua nits + 1 pre-existing JET @test_broken (tracked in #36) are unchanged. Core suite (539 tests) still passes after the source rewrites.

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