sagemathgh-39469: small improvement in `classically_highest_weight_ve…

…ctors`

The change is to avoid insertions and removals at the beginning of a
list as these operations require linear time in the length of the list.
We instead build the reverse path (append and pop at the end of the list
in constant time) and use method `reversed` when needed.

### 📝 Checklist

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- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: sagemath#39469
Reported by: David Coudert
Reviewer(s): Frédéric Chapoton

build/pkgs/configure/checksums.ini

@@ -1,3 +1,3 @@
 tarball=configure-VERSION.tar.gz
-sha1=86711d4cbef2cd4e7bb4afcde36965e5dea908e0
-sha256=9793cf92ebdceb09050a585294de93c242c033745a0012cae1bd301d307a45df
+sha1=2a6cd0b57346c92a73fc14246672abd6f150b423
+sha256=a732b3abcdf5f63995c63b765af00bfeed8efb67f1f451caac3ae2f48a105ad4

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-efc0914cd8d72a9bdfdcca4511b55e290b9b6674
+3735a1f77361171f19919b1651e14a56332c41ba

src/sage/categories/loop_crystals.py

@@ -773,16 +773,17 @@ def classically_highest_weight_vectors(self):
                     except StopIteration:
                         it.pop()
                         if path:
-                            path.pop(0)
+                            path.pop()
                         continue
 
-                    b = self.element_class(self, [x] + path)
+                    path.append(x)
+                    b = self.element_class(self, reversed(path))
                     if not b.is_highest_weight(index_set=I0):
+                        path.pop()
                         continue
-                    path.insert(0, x)
                     if len(path) == n:
                         ret.append(b)
-                        path.pop(0)
+                        path.pop()
                     else:
                         it.append(iter(self.crystals[-len(path) - 1]))
                 return tuple(ret)