Use build_info_path in load_build_info, update TOML parsing logic

[palinatolmach]

This PR addresses the

  File "/Users/palina/rv/kontrol/src/kontrol/solc.py", line 501, in load_build_info
    build_info = json.loads(max(build_info_files, key=os.path.getmtime).read_text())
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: max() iterable argument is empty

error which occurs if the project uses a non-default build_info_path in foundry.toml:

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
build_info_path = 'artifacts/build-info'
extra_output = ['storageLayout']

[profile.kontrol-properties]
out = 'out-kontrol-properties'

In addition, it also updates the profile function in foundry.py so that if the key is not defined in the current profile but it is set in the default profile, the default value (and not an empty string) is used:

    @property
    def profile(self) -> dict[str, Any]:
        profile_name = os.getenv('FOUNDRY_PROFILE', default='default')

        current_profile = self._toml['profile'].get(profile_name, {})
        default_profile = self._toml['profile'].get('default', {})

        return {**default_profile, **current_profile}