fix(patches): RcppParallel disable-TBB source patch (was a no-op env var)

The previous entry set env RCPP_PARALLEL_USE_TBB=0, but RcppParallel reads that
only as a compile -D flag, not from the environment — so it was a no-op and the
bundled Intel TBB build still ran (and hung on musl / newer toolchains).

Replace it with a source patch on src/Makevars.in that leaves USE_TBB unset
(skipping the bundled TBB build) and forces -DRCPP_PARALLEL_USE_TBB=0 so the
sources use the TinyThread backend. Verified in a Linux container: RcppParallel
installs with no bundled-TBB build (* DONE (RcppParallel)).

local/patches/RcppParallel/disable-tbb.patch

@@ -0,0 +1,16 @@
+diff --git a/src/Makevars.in b/src/Makevars.in
+index be8445f..faee771 100644
+--- a/src/Makevars.in
++++ b/src/Makevars.in
+@@ -60,7 +60,10 @@ else
+ 	endif
+ 
+ 	ifeq ($(UNAME), Linux)
+-		USE_TBB=Linux
++		# bincraft patch: the bundled Intel TBB build hangs/fails on musl (Alpine)
++		# and newer toolchains (g++ 15). Skip it (leave USE_TBB unset) and force the
++		# TinyThread backend so RcppParallel still builds.
++		PKG_CXXFLAGS += -DRCPP_PARALLEL_USE_TBB=0
+ 	endif
+ 
+ 	ifeq ($(UNAME), SunOS)

local/patches/registry.json

@@ -3,10 +3,10 @@
     "package": "RcppParallel",
     "versions": "*",
     "platforms": ["alpine", "ubuntu-2604"],
-    "env": { "RCPP_PARALLEL_USE_TBB": "0" },
+    "env": {},
     "configure_args": [],
     "makevars": {},
-    "patch": null,
-    "reason": "bundled Intel TBB fails to build on musl and on newer toolchains (e.g. g++ 15 on ubuntu-2604); disabling TBB falls back to TinyThread"
+    "patch": "RcppParallel/disable-tbb.patch",
+    "reason": "bundled Intel TBB build hangs/fails on musl (Alpine) and newer toolchains (g++ 15 on ubuntu-2604); patch unsets USE_TBB and forces -DRCPP_PARALLEL_USE_TBB=0 so RcppParallel skips the bundled build and uses the TinyThread backend"
   }
 ]