IPv6 endpoint address not bracketed in URL construction (REC1b2)

[paddybyers]

Spec point

• REC1b2: When `endpoint` is an IPv6 address (e.g., `::1`), the library should treat it as an explicit hostname and construct valid URLs.

Observed behaviour

`getPrimaryDomainFromEndpoint('::1')` correctly identifies the address as an explicit hostname via `isFqdnIpOrLocalhost`, but URL construction produces `https://::1:443/time` instead of the valid `https://[::1]:443/time`. The missing brackets cause an "Invalid URI" error.

Failing test

Test	Expected	Actual
`REC1b2 - endpoint as IPv6 address`	Valid request to `[::1]`	`Invalid URI: https://::1:443/time`

Reproduction

```bash
RUN_DEVIATIONS=1 npx mocha --grep "REC1b2" test/uts/rest/fallback.test.ts
```

From PR #2191, branch `uts-rest`.

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