Fix CI runner crashes: cycle detection, SymbolicUtils ≥ 4.27 floor, macOS arm64

[ChrisRackauckas-Claude]

Fixes the things that prevent the difficult-test job from producing a meaningful per-integral signal. Does not touch the test gate — count(x -> x != 0, …) == 0 stays as the strict bar, so CI will still red-fail on integrals the engine doesn't yet solve. Those are genuine engine work items to address separately; this PR just stops the runner from aborting before they can be observed.

What's in scope

1. ci: drop hard-coded x64 arch so macOS arm64 runners work
GitHub's macos-latest is now Apple Silicon, so setup-julia@v3 errored out on arch: x64 before the test step ever ran. Drop the arch matrix axis and let setup-julia auto-detect per OS.

2. fix(rule_based): break multi-rule rewrite cycles in repeated_prewalk
Some Apostol rationals (e.g. (2+x)/(x+x²), 1/(x·(1+x²)²)) sent the rule-based engine into a 2-step rewrite cycle: rule A rewrites ∫f to ∫g, rule B rewrites ∫g back to ∫f. apply_rule's existing result === problem guard only catches single-step identity loops, so repeated_prewalk recursed forever and eventually overflowed the stack deep enough to fault Julia's type inference of RuleRewriteError itself — signal (6.-6): Aborted, no recovery possible from any user-level try/catch. Thread a visited::Set through the linear rewrite chain; on a re-visit, return the integral unevaluated (which the suite then classifies as a normal [ fail ]). Sibling subtrees start with a fresh set.

3. build: require SymbolicUtils ≥ 4.27
v4.27 is the first release containing the poly_to_gcd_form concrete-eltype fix (JuliaSymbolics/SymbolicUtils.jl#906). Without it, simplify(diff; expand=true) inside the difficult-test verifier throws MethodError(MP.Term{T,M} where T, …) on several Apostol rationals (e.g. (2-x+2x²-x³+x⁴)/((-1+x)·(2+x²)²), 1/(-1+x²)²), masking the underlying integration result with a verifier crash.

What's not in scope

• Changes to the test gate. count(x -> x != 0, …) == 0 is preserved as-is.
• Whitelisting / skipping integrals the engine can't currently solve.
• Engine coverage work to actually pass the strict bar.

So CI on this PR is expected to be red until the engine learns to solve the remaining Apostol cases — and that red is informative now, not a SIGABRT.

Local validation (Julia 1.10.11, ubuntu, this branch)

With all three fixes in:

[Rule Based] Integration of 177 functions: 93 ok, 50 fail, 34 maybe-fail, 0 errored
[Risch]      Integration of 177 functions: 29 ok, 134 fail, 14 maybe-fail, 0 errored
Wallclock: ~2m46s

Compared to main against the same SymbolicUtils v4.27.0: SIGABRT partway through Apostol when the cycle bug overflows the stack. So 'completes the suite + 122/354 fails' is strictly more informative than the current 'aborts mid-suite with no scoreboard'.

Test plan

• Easy tests pass on Julia 1.10.11 locally (94 pass, 1 pre-existing broken).
• Difficult-test runner runs to completion on Julia 1.10.11 locally (no SIGABRT, no MethodError, no [except] events). The strict bar still fails on the unsolved integrals — that's the intended state.
• Two known cyclic integrals ((2+x)/(x+x²), 1/(x·(1+x²)²)) terminate cleanly instead of hanging/SIGABRTing.
• CI red here on the genuine coverage gap (expected); each crash class fixed.

Draft PR — please ignore until reviewed by @ChrisRackauckas.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 20.98%. Comparing base (85a221a) to head (de8404a).
⚠️ Report is 21 commits behind head on main.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
+ Coverage   13.91%   20.98%   +7.07%     
==========================================
  Files          22       22              
  Lines        4291     4293       +2     
==========================================
+ Hits          597      901     +304     
+ Misses       3694     3392     -302     

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