Change implementation to mimic poetry-export-plugin

[vchrombie]

The current implementation fetches the dependency name and version from the pyproject.toml file using tomli. Currently, this would support only three formats i.e, foo = '^n.n.n', foo = '>=n.n.n', foo = 'n.n.n'.

The goal of this issue is to change the implementation to something like how poetry-export-plugin and python-poetry/poetry-plugin-export#3 works. It needs to extract the dependency name and version from the poetry.lock file which makes it independent of the pyproject.toml file and also supports all the formats, since poetry converts them to dependency name and version format in the lock file.