fix: dependency resolver on windows only works when --enable_runfiles and --windows_enable_symlinks is used (#2457)

`compile_pip_requirements` doesn't work as expected on Windows unless
both `--enable_runfiles` and `--windows_enable_symlinks` are used. Both
options default to off on Windows because the filesystem on Windows
makes setting up the runfiles directories with actual files very slow.
This means that anyone on Windows with a default set up has to search
around the Github issues to try and figure out why things don't work as
advertised.

The `dependency_resolver.py` doesn't inherently require these options,
it just had two bugs that prevented it from working.

1. calling pip_compile exits the whole program so it never gets to run
the code that should copy the output to the source tree. Things just
happen to work on linux because the runfiles are symlinks, and it does
not need to copy anything.
2. it assumed the `runfiles` resolved file would be in the runfiles
tree, but on Windows, when `--enable_runfiles` is not set, it actually
gets resolved to a file in the source tree.

Before:
```sh
bazel run //third_party/python:requirements.update
Starting local Bazel server and connecting to it...
INFO: Invocation ID: 8aa3e832-78ce-4999-912b-c43e7ca3212b
INFO: Analyzed target //third_party/python:requirements.update (129 packages loaded, 9563 targets configured).
INFO: Found 1 target...
Target //third_party/python:requirements.update up-to-date:
  bazel-bin/third_party/python/requirements.update.zip
  bazel-bin/third_party/python/requirements.update.exe
INFO: Elapsed time: 60.964s, Critical Path: 0.77s
INFO: 8 processes: 2 remote cache hit, 6 internal.
INFO: Build completed successfully, 8 total actions
INFO: Running command line: bazel-bin/third_party/python/requirements.update.exe '--src=_main/third_party/python/requirements.txt' _main/third_party/python/requirements_lock.txt //third_party/python:requirements.update '--resolver=backtracking' --allow-unsafe --generate-hashes '--requirements-windows=_main/third_party/python/requirements_windows.txt' --strip-extras
Updating third_party/python/requirements_windows.txt
Error: Could not open file 'third_party/python/requirements_windows.txt': No such file or directory
```

After:
```sh
bazel run //third_party/python:requirements.update
INFO: Invocation ID: 39f999a0-6c1d-4b2c-a1be-3d71e838916a
INFO: Analyzed target //third_party/python:requirements.update (5 packages loaded, 45 targets configured).
INFO: Found 1 target...
Target //third_party/python:requirements.update up-to-date:
  bazel-bin/third_party/python/requirements.update.zip
  bazel-bin/third_party/python/requirements.update.exe
INFO: Elapsed time: 5.410s, Critical Path: 4.79s
INFO: 2 processes: 1 internal, 1 local.
INFO: Build completed successfully, 2 total actions
INFO: Running command line: bazel-bin/third_party/python/requirements.update.exe '--src=_main/third_party/python/requirements.txt' _main/third_party/python/requirements_lock.txt //third_party/python:requirements.update '--resolver=backtracking' --allow-unsafe --generate-hashes '--requirements-windows=_main/third_party/python/requirements_windows.txt' --strip-extras
Updating third_party/python/requirements_windows.txt
#
# This file is autogenerated by pip-compile with Python 3.13
# by the following command:
#
#    bazel run //third_party/python:requirements.update
#
mpmath==1.3.0 \
    --hash=sha256:7a28eb2a9774d00c7bc92411c19a89209d5da7c4c9a9e227be8330a23a25b91f \
    --hash=sha256:a0b2b9fe80bbcd81a6647ff13108738cfb482d481d826cc0e02f5b35e5c88d2c
    # via sympy
sympy==1.13.3 \
    --hash=sha256:54612cf55a62755ee71824ce692986f23c88ffa77207b30c1368eda4a7060f73 \
    --hash=sha256:b27fd2c6530e0ab39e275fc9b683895367e51d5da91baa8d3d64db2565fec4d9
    # via -r G:/projects/bedrock-engine/third_party/python/requirements.txt
```
And `//third_part/python:requirements_windows.txt` is updated.

Fixes #1943 
Fixes #1431

---------

Co-authored-by: Ignas Anikevicius <240938+aignas@users.noreply.github.com>