Option to support poetry export packages only specified in pyproject.toml, but no related upstreams

pyproject.toml:

[tool.poetry.dependencies]
python = "^3.10"
httpx = "^0.23.3"

now poetry export output:

anyio==3.6.2 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:25ea0d673ae30af41a0c442f81cf3b38c7e79fdc7b60335a4c14e05eb0947421 \
    --hash=sha256:fbbe32bd270d2a2ef3ed1c5d45041250284e31fc0a4df4a5a6071842051a51e3
certifi==2022.12.7 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:35824b4c3a97115964b408844d64aa14db1cc518f6562e8d7261699d1350a9e3 \
    --hash=sha256:4ad3232f5e926d6718ec31cfc1fcadfde020920e278684144551c91769c7bc18
h11==0.14.0 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:8f19fbbe99e72420ff35c00b27a34cb9937e902a8b810e2c88300c6f0a3b699d \
    --hash=sha256:e3fe4ac4b851c468cc8363d500db52c2ead036020723024a109d37346efaa761
httpcore==0.16.3 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:c5d6f04e2fc530f39e0c077e6a30caa53f1451096120f1f38b954afd0b17c0cb \
    --hash=sha256:da1fb708784a938aa084bde4feb8317056c55037247c787bd7e19eb2c2949dc0
httpx==0.23.3 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:9818458eb565bb54898ccb9b8b251a28785dd4a55afbc23d0eb410754fe7d0f9 \
    --hash=sha256:a211fcce9b1254ea24f0cd6af9869b3d29aba40154e947d2a07bb499b3e310d6
idna==3.4 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:814f528e8dead7d329833b91c5faa87d60bf71824cd12a7530b5526063d02cb4 \
    --hash=sha256:90b77e79eaa3eba6de819a0c442c0b4ceefc341a7a2ab77d7562bf49f425c5c2
rfc3986[idna2008]==1.5.0 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:270aaf10d87d0d4e095063c65bf3ddbc6ee3d0b226328ce21e036f946e421835 \
    --hash=sha256:a86d6e1f5b1dc238b218b012df0aa79409667bb209e58da56d0b94704e712a97
sniffio==1.3.0 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:e60305c5e5d314f5389259b7f22aaa33d8f7dee49763119234af3755c55b9101 \
    --hash=sha256:eecefdce1e5bbfb7ad2eeaabf7c1eeb404d7757c379bd1f7e5cce9d8bf425384

Maybe we can support option to output top packages that only specified by pyproject.toml directly(the example above is just httpx)

Expected export:

httpx==0.23.3 ; python_version >= "3.10" and python_version < "4.0" \
    --hash=sha256:9818458eb565bb54898ccb9b8b251a28785dd4a55afbc23d0eb410754fe7d0f9 \
    --hash=sha256:a211fcce9b1254ea24f0cd6af9869b3d29aba40154e947d2a07bb499b3e310d6

Reproduce the example with the provided pyproject.toml and poetry export command, then trace how exported dependencies are selected. The change is complete when the export contains only packages declared directly in pyproject.toml, such as httpx, while preserving its version marker and hashes.