misc: use activated venv dir if any, and add back project venv export (…

…#3630)

This change lets us use the activated venv, if any, for all our make
commands. In order to make it work, I had to add back the export,
because otherwise the inner uv commands would complain about the fact
that the current venv is not the same as the project venv, which is
.venv if not overridden.

Makefile

@@ -6,7 +6,9 @@ COVERAGE_FILE ?= .coverage
 
 # allow overriding the name of the venv directory
 VENV_DIR ?= .venv
-UV_PROJECT_ENVIRONMENT=${VENV_DIR}
+
+# use activated venv if any
+export UV_PROJECT_ENVIRONMENT=$(if $(VIRTUAL_ENV),$(VIRTUAL_ENV),$(VENV_DIR))
 
 # allow overriding which extras are installed
 VENV_EXTRAS ?= --extra gui --extra dev --extra jax --extra riscv