[CI] Update build image baseline to GCC 11 and CUDA 12.8 (#79340)

* Update CI build image GCC to 11

* Build Python from source in CI image

* Move Python source build into Ubuntu20 Dockerfile

* [CI] Update build image to CUDA 12.8

* Fix GCC 11 install in CI build image

* Use CUDA 12.6 build image for SM70 TensorRT

* Use mirror for GCC 11 source download

* Revert "Use mirror for GCC 11 source download"

This reverts commit 2e91ecd5394d3793c926e073a72b676ef6ff8c0b.

* Use TRT 8 build image for P4 inference

* Use CUDA 12.4 for GCC 11 build image

* Use CUDA 12.8 build image without TensorRT

* Enable Python faulthandler for CE framework test

* Avoid overriding system libstdc++ in GCC 11 image

* Include docker build scripts in image cache key

* test: constrain scipy for coverage tests

* ci: expose GCC 11 libstdc++ in build image

* ci: prefer GCC 11 libstdc++ during build

* ci: add CE saveload abort diagnostics

* ci: install CUDA CCCL headers in CE image

* ci: keep GCC runtime first in test jobs

* ci: remove CE debug env exports

* ci: guard docker build script hash

* ci: tune api benchmark library path order