exp: move the precompilation toolchain disabling shortcircuit down the callstack

Stil not working:
```
$ bazel cquery 'deps(@dev_pip//charset_normalizer)' --transitions=lite --extra_toolchains=@bazel_tools//tools/python:autodetecting_toolchain | grep "toolchain dependency"

Computing main repo mapping:
Loading:
Loading: 0 packages loaded
WARNING: Build option --extra_toolchains has changed, discarding analysis cache (this can be expensive, see https://bazel.build/advanced/performance/iteration-speed).
Analyzing: target @@_main~pip_internal~dev_pip//charset_normalizer:charset_normalizer (0 packages loaded, 0 targets configured)
INFO: Analyzed target @@_main~pip_internal~dev_pip//charset_normalizer:charset_normalizer (1 packages loaded, 1530 targets configured).
INFO: Found 1 target...
  [toolchain dependency]#@@_main~python~python_3_11_x86_64-unknown-linux-gnu//:py_exec_tools_toolchain#NoTransition ->
  [toolchain dependency]#@bazel_tools//tools/python:_autodetecting_py_runtime_pair#NoTransition ->
INFO: Elapsed time: 0.342s, Critical Path: 0.00s
INFO: 0 processes.
INFO: Build completed successfully, 0 total actions
```

Author: aignas

python/private/common/common_bazel.bzl

@@ -65,14 +65,7 @@ def maybe_precompile(ctx, srcs):
         * `py_to_pyc_map`: dict of src File input to pyc File output. If a source
           file wasn't precompiled, it won't be in the dict.
     """
-
-    # The exec tools toolchain and precompiler are optional. Rather than
-    # fail, just skip precompiling, as its mostly just an optimization.
-    exec_tools_toolchain = ctx.toolchains[EXEC_TOOLS_TOOLCHAIN_TYPE]
-    if exec_tools_toolchain == None or exec_tools_toolchain.exec_tools.precompiler == None:
-        precompile = PrecompileAttr.DISABLED
-    else:
-        precompile = PrecompileAttr.get_effective_value(ctx)
+    precompile = PrecompileAttr.get_effective_value(ctx)
 
     source_retention = PrecompileSourceRetentionAttr.get_effective_value(ctx)
 
@@ -98,6 +91,12 @@ def maybe_precompile(ctx, srcs):
             (source_retention == PrecompileSourceRetentionAttr.OMIT_IF_GENERATED_SOURCE and not is_generated_source)
         )
         if should_precompile:
+            # The exec tools toolchain and precompiler are optional. Rather than
+            # fail, just skip precompiling, as its mostly just an optimization.
+            exec_tools_toolchain = ctx.toolchains[EXEC_TOOLS_TOOLCHAIN_TYPE]
+            if exec_tools_toolchain == None or exec_tools_toolchain.exec_tools.precompiler == None:
+                precompile = PrecompileAttr.DISABLED
+                break
             pyc = _precompile(ctx, src, use_pycache = keep_source)
             result.pyc_files.append(pyc)
             result.py_to_pyc_map[src] = pyc