Ensure that the hostname has a port number when building pushpin routes

[harmony7]

Change summary

This PR adds a port number if not specified when building Pushpin routes from fastly.toml, when experimental pushpin is enabled.

Given the following fastly.toml file:

[local_server.pushpin]
enable = true

[local_server.backends]
[local_server.backends.origin]
url = "https://example.com/"
override_host = "example.com"

[local_server.backends.self]
url = "http://localhost:7676/"
override_host = "localhost:7676"

Before the fix, without the port number, Pushpin throws an error during initialization:

routes

id=origin example.com,over_http,ssl,host=example.com
id=self localhost:7676,over_http,host=localhost:7676

pushpin-proxy.log

[DEBUG] 2026-01-23 14:56:04.572 starting...
[WARN] 2026-01-23 14:56:04.576 /var/folders/ww/gnnpyf154zn_rd2fy12th2zxljyppv/T/pushpin-routes-0c353e5c:1: target bad format
[DEBUG] 2026-01-23 14:56:04.576 routes by domain:
[INFO] 2026-01-23 14:56:04.576 routes loaded with 1 entries
[DEBUG] 2026-01-23 14:56:04.580 worker 0: started
[INFO] 2026-01-23 14:56:04.580 started

After this fix:

routes

id=origin example.com:443,over_http,ssl,host=example.com
id=self localhost:7676,over_http,host=localhost:7676

pushpin-proxy.log

[DEBUG] 2026-01-23 18:33:49.755 starting...
[DEBUG] 2026-01-23 18:33:49.757 routes by domain:
[INFO] 2026-01-23 18:33:49.757 routes loaded with 2 entries
[DEBUG] 2026-01-23 18:33:49.760 worker 0: started
[INFO] 2026-01-23 18:33:49.760 started

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User Impact

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[anthony-gomez-fastly]

LGTM