purevpn: split selector filters into dedicated PR

[reedog117]

[Generated by Codex] Description

This PR splits the PureVPN selector functionality out of qdm12#3165 and targets the codex/purevpn-deb-updater base branch.

Included in this PR

• Adds PureVPN selector fields in server selection settings:
  • purevpn_server_types (supports regular, portforwarding, quantumresistant, obfuscation, p2p)
  • purevpn_country_codes
  • purevpn_location_codes
• Adds parsing/normalization and validation for these selectors.
• Adds selector-aware filtering in provider and storage filtering paths.
• Adds no-server-found formatting output for the selector filters.
• Adds focused tests:
  • internal/configuration/settings/serverselection_purevpn_test.go
  • internal/storage/filter_purevpn_test.go
  • updates to existing internal/provider/utils/filtering_test.go

Notes

• This PR intentionally builds on top of codex/purevpn-deb-updater and does not include the base updater/deb extraction changes already in that branch.

Local validation

• go test ./internal/configuration/settings ./internal/provider/utils ./internal/storage ./internal/provider/purevpn/...
• go test ./internal/openvpn
• go build ./cmd/gluetun