roll: third_party/pigweed: bazel: Use Python toolchain in custom rules

This will make the bzlmod transition smoother (by removing the @python3
reference: in the bzlmod version of rules_python this repo doesn't exist
any more). The Python toolchain is the right way to access the
interpreter anyway.

This is a reland of http://pwrev.dev/224272. The original change had an
unlucky mid-air collision with http://pwrev.dev/204199. However, I also
took the opportunity to fix the toolchain type to the
exec_tools_toolchain_type (see https://pwbug.dev/258836641#comment59 for
more).

Original-Bug: 258836641
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/224298
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: e3076ba724ed431..e45ec8f7c2d1e77
Roller-URL: https://ci.chromium.org/b/8742001426880540529
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ifc07722af2c04ae425f8bb9ad9be31eccfbb8723
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/224631
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index e3076ba..e45ec8f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e3076ba724ed4314daee7d982be6961e19b3392f
+Subproject commit e45ec8f7c2d1e77258bd1cc9becdc5191bead5bf