feat(releases): open the fzf picker before fetch

[barrettruth]

Summary

• open the fzf release picker immediately before the release fetch completes so browse, copy, filter, and delete actions are available right away
• reuse a single fetched release list across the all, draft, and prerelease views since those states are just local filters of the same dataset
• add regressions for the instant-open release path and for filter switches reusing the shared cached release list

Test plan

• nix --extra-experimental-features "nix-command flakes" develop .#ci --command busted spec/pickers_spec.lua spec/fzf_picker_spec.lua
• nix --extra-experimental-features "nix-command flakes" develop .#ci --command stylua --check lua/forge/pickers.lua spec/pickers_spec.lua
• nix --extra-experimental-features "nix-command flakes" develop .#ci --command selene lua/forge/pickers.lua spec/pickers_spec.lua
• nix --extra-experimental-features "nix-command flakes" develop .#ci --command lua-language-server --check lua/forge/pickers.lua spec/pickers_spec.lua
• nix --extra-experimental-features "nix-command flakes" develop .#ci --command busted