[Bug]: Update `flit-core` dependency in `meta.yaml` to 4.x

[harryswift01]

Bug Report

The meta.yaml conda build requirement still constrains flit-core to 3.x, while the project has been updated to use Flit 4.

To Reproduce

YAML configuration

requirements:
  host:
    - python >=3.12
    - pip
    - flit-core >=3.4,<4

The project build configuration now requires:

[build-system]
requires = ["flit_core >=4,<5"]
build-backend = "flit_core.buildapi"

Expected Behaviour

The conda recipe should use the same Flit Core major version as the project build configuration:

requirements:
  host:
    - python >=3.12
    - pip
    - flit-core >=4,<5

Additional Context

The Flit dependencies were updated to 4.x to resolve the PyPI publishing issue, but the corresponding flit-core requirement in meta.yaml was not updated.