fix(toolchain): fix crash on Windows when precompiling is enabled

[rdesgroppes]

python/private/py_executable.bzl's _maybe_add_test_main_validation fix (#4079) noted precompile.bzl as a remaining user of the same exec_interpreter relocation issue, needing the same migration.

There was no existing test exercising _precompile's action at all: tests/base_rules/precompile's suite is analysis_test-only, checking declared providers, never actually running the precompiler.
Reproducing this on Windows therefore required a real bazel build, via the new test_precompile_enabled_succeeds:

bazel test \
  //tests/base_rules/precompile:test_precompile_enabled_succeeds
...
ERROR: .../tests/base_rules/precompile/BUILD.bazel:3:22: Python
 precompiling .../test_precompile_enabled_succeeds_main.py into
 .../test_precompile_enabled_succeeds_main.cpython-311.pyc
 failed: Worker process did not return a WorkResponse:
---8<---8<--- Start of log, file at
 .../multiplex-worker-1-PyCompile.log ---8<---8<---
(empty)
---8<---8<--- End of log ---8<---8<---

The worker crashes at startup, unable to find its DLLs, before it can write anything to its own log or respond over the worker protocol.

_precompile now uses actions_run() with exec_runtime, exactly as _maybe_add_test_main_validation does, instead of exec_tools_info.exec_interpreter[DefaultInfo].files_to_run.

Reproducing and fixing this also uncovered two more problems, both specific to the precompiler's worker mode and unrelated to exec_interpreter.

First, tools/precompiler/precompiler.py's persistent worker reads each JSON request as a single line via asyncio.StreamReader, whose default 64KiB limit is exceeded once every interpreter distribution file, previously hidden by relocation into a much smaller symlink tree, shows up as an actual, individually-digested action input:

ValueError: Separator is not found, and chunk exceed the limit

A CPython 3.11 distribution's ~2,260 inputs measure ~470KiB this way; 1 << 22 (4MiB) leaves ample headroom.

Second, the worker's default implementation, _AsyncPersistentWorker, can't start on Windows at all: asyncio's ProactorEventLoop fails to wrap stdin/stdout as pipe transports, with:

OSError: [WinError 6] The handle is invalid

Bazel gives workers anonymous pipes (CreatePipe) for stdio, which never support overlapped I/O, so asyncio's ProactorEventLoop can't register them with an I/O completion port.
This is unrelated to precompiling's relocation bug: nothing exercises this worker on Windows today.
_SerialPersistentWorker, the blocking-I/O alternative already present in the file, has no such issue, so --worker_impl now defaults to serial on Windows.

tests/base_rules/precompile:test_precompile_enabled_succeeds is a real, executing py_test with precompile = "enabled", added alongside the analysis-only suite to close this gap: it forces the precompiler action to actually run, and needs no CI wiring since it carries no tag excluding it from the existing Windows job's default test sweep.