Move heavy AD backends out of root [extras] into group envs (#62)

FastPower's optional AD backends (Enzyme, ForwardDiff, Mooncake,
ReverseDiff, Tracker) plus their test-only support deps (EnzymeTestUtils,
StableRNGs) were declared in the root Project.toml's [extras]/[targets].test.
Because the folder-model Core group and the Enzyme group folder both run in
the main test env, this pulled the full joint AD graph into every
root/Core resolve — including the Downgrade lane, which had to floor-resolve
all five backends together against the base package.

Move each backend into the group env whose files actually `using` it:

* test/AD/Project.toml (new) — ForwardDiff/ReverseDiff/Tracker/Mooncake for
  the relocated test/AD/other_ad_engines_tests.jl (was a loose top-level Core
  file, now its own AD group declared in test_groups.toml).
* test/Enzyme/Project.toml (new) — Enzyme/EnzymeTestUtils/StableRNGs for the
  existing test/Enzyme/ group folder (which previously had no Project.toml and
  so resolved against the root env).

Root [extras]/[targets].test keeps only SafeTestsets/SciMLTesting/Test (the
harness + Core deps). Weakdep [compat] entries (Enzyme, ForwardDiff, Mooncake,
ReverseDiff, Tracker) stay since they still gate package extensions; the
extra-only compats (EnzymeTestUtils, StableRNGs) are removed to avoid dangling.

Under the folder-discovery harness each group folder auto-activates its own
Project.toml, so no runtests.jl wiring changes are needed. The root/Core
Downgrade lane no longer floor-resolves any AD backend; cross-backend AD tests
are unchanged (AD 4/4, Enzyme 88/88, Core 1205/1205 all pass locally).

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>

Author: ChrisRackauckas-Claude

Project.toml

@@ -25,30 +25,21 @@ FastPowerTrackerExt = "Tracker"
 
 [compat]
 Enzyme = "0.13.89"
-EnzymeTestUtils = "0.2"
 ForwardDiff = "0.10, 1"
 Measurements = "2.5"
 MonteCarloMeasurements = "1"
 Mooncake = "0.4, 0.5"
 ReverseDiff = "1.14"
 SafeTestsets = "0.1, 1"
 SciMLTesting = "1"
-StableRNGs = "1"
 Test = "1"
 Tracker = "0.2"
 julia = "1.10"
 
 [extras]
-Enzyme = "7da242da-08ed-463a-9acd-ee780be4f1d9"
-EnzymeTestUtils = "12d8515a-0907-448a-8884-5fe00fdf1c5a"
-ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
-Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
-ReverseDiff = "37e2e3b7-166d-5795-8a7a-e32c996b4267"
 SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 SciMLTesting = "09d9d899-5365-40a9-917a-5f67fddea283"
-StableRNGs = "860ef19b-820b-49d6-a774-d7a799459cd3"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
-Tracker = "9f7883ad-71c0-57eb-9f7f-b5c9e6d3789c"
 
 [targets]
-test = ["Enzyme", "EnzymeTestUtils", "ForwardDiff", "Mooncake", "ReverseDiff", "SafeTestsets", "SciMLTesting", "StableRNGs", "Test", "Tracker"]
+test = ["SafeTestsets", "SciMLTesting", "Test"]

test/AD/Project.toml

@@ -0,0 +1,23 @@
+[deps]
+FastPower = "a4df4552-cc26-4903-aec0-212e50a0e84b"
+ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
+ReverseDiff = "37e2e3b7-166d-5795-8a7a-e32c996b4267"
+SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
+SciMLTesting = "09d9d899-5365-40a9-917a-5f67fddea283"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+Tracker = "9f7883ad-71c0-57eb-9f7f-b5c9e6d3789c"
+
+[sources]
+FastPower = {path = "../.."}
+
+[compat]
+FastPower = "1"
+ForwardDiff = "0.10, 1"
+Mooncake = "0.4, 0.5"
+ReverseDiff = "1.14"
+SafeTestsets = "0.1, 1"
+SciMLTesting = "1"
+Test = "1"
+Tracker = "0.2"
+julia = "1.10"

test/other_ad_engines_tests.jl test/AD/other_ad_engines_tests.jltest/other_ad_engines_tests.jl renamed to test/AD/other_ad_engines_tests.jl

@@ -0,0 +1,21 @@
+[deps]
+Enzyme = "7da242da-08ed-463a-9acd-ee780be4f1d9"
+EnzymeTestUtils = "12d8515a-0907-448a-8884-5fe00fdf1c5a"
+FastPower = "a4df4552-cc26-4903-aec0-212e50a0e84b"
+SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
+SciMLTesting = "09d9d899-5365-40a9-917a-5f67fddea283"
+StableRNGs = "860ef19b-820b-49d6-a774-d7a799459cd3"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[sources]
+FastPower = {path = "../.."}
+
+[compat]
+Enzyme = "0.13.89"
+EnzymeTestUtils = "0.2"
+FastPower = "1"
+SafeTestsets = "0.1, 1"
+SciMLTesting = "1"
+StableRNGs = "1"
+Test = "1"
+julia = "1.10"

test/Enzyme/Project.toml

@@ -1,6 +1,9 @@
 [Core]
 versions = ["lts", "1", "pre"]
 
+[AD]
+versions = ["lts", "1"]
+
 [Enzyme]
 versions = ["lts", "1"]