feat: add port-range support for haproxy-route-tcp

[swetha1654]

Summary

Implements port-range support for the haproxy-route-tcp interface as requested in issue #525.

This allows haproxy-route-tcp requirers to specify a port range (e.g. "10500-10600") instead of a single port. HAProxy will bind to the entire range and forward each incoming connection to the backend on the same port (1:1 passthrough via set-dst-port fc_dst_port).

Changes

Library (lib/charms/haproxy/v1/haproxy_route_tcp.py, LIBPATCH 3→4)

• Added port_range: Optional[str] field to TcpRequirerApplicationData
• Added validators:
  • validate_port_or_port_range: exactly one of port or port_range must be set; format ^\d+-\d+$ with start < end
  • assign_default_backend_port: raises if backend_port is set with port_range
  • sni_set_when_not_enforcing_tls: raises if sni is set with port_range
  • tls_terminate_requires_no_port_range: raises if tls_terminate=True with port_range (passthrough mode only)
• Updated check_ports_unique to expand ranges for overlap detection
• Updated provide_haproxy_route_tcp_requirements signature to accept port_range
• Fixed update_relation_data guard to also accept port_range (was checking only port)

State (src/state/haproxy_route_tcp.py, src/state/haproxy_route.py)

• HaproxyRouteTcpServer.port is now Optional[int] (None for port-range passthrough)
• HAProxyRouteTcpBackend.servers: sets port=None, check=None for port_range backends
• HAProxyRouteTcpFrontend: new port_range field, frontend_name, bind_address, all_frontend_ports properties
• parse_haproxy_route_tcp_requirers_data: groups by port_range string as key
• check_tcp_http_port_conflicts / valid_tcp_frontends: expand ranges for conflict detection

Template (templates/haproxy_route_tcp.cfg.j2)

• Port-range frontend uses bind [::]:START-END v4v6
• Adds tcp-request session set-dst-port fc_dst_port for dynamic port passthrough
• Backend server rendered as server NAME IP:0 (port 0 = use set-dst-port value)
• Health checks automatically disabled for port-range backends (port 0 incompatible)

Charm (src/charm.py)

• set_ports and endpoint publishing use all_frontend_ports to handle both single ports and ranges

HAProxy mechanism

frontend haproxy_route_tcp_10500_10600
    bind [::]:10500-10600 v4v6
    mode tcp
    tcp-request session set-dst-port fc_dst_port
    default_backend haproxy_route_tcp_10500_10600_default_backend

backend haproxy_route_tcp_10500_10600_default_backend
    mode tcp
    server myapp-0 10.0.0.1:0

Tests

• 11 new unit tests in tests/unit/test_haproxy_route_tcp_lib.py
• 5 new unit tests in tests/unit/test_state.py
• 1 new integration test test_haproxy_route_tcp_port_range — locally verified passing

Closes #525