### Summary
This PR makes `Session.ValidateServerEndpoints()` compare
`ServerEndpoints` and `UserIdentityTokens` as unordered sets and adds
regression tests that verify `OpenAsync()` no longer rejects legal
servers that return the same endpoint data in a different order.
### Problem
According to OPC UA Part 4, the client validates the endpoint set
returned by `CreateSessionResponse.ServerEndpoints` against the endpoint
set observed during discovery. The specification describes these values
as a set of endpoint descriptions filtered by the relevant transport
profile, not as an ordered array that must preserve the exact
discovery-time enumeration order.
Previously, `Session.ValidateServerEndpoints()` first checked the
endpoint count and then compared `m_discoveryServerEndpoints[ii]`
against `serverEndpoints[ii]` by index. It also compared
`UserIdentityTokens[jj]` by index within each endpoint. As a result, a
server that returned the same legal endpoints in a different order, or
returned the same token policies in a different order within an
endpoint, could be rejected with `BadSecurityChecksFailed` even though
the endpoint data itself had not changed.
### Changes
- Replace index-based `ServerEndpoints` validation with unordered
matching based on the same endpoint fields already validated by the
client.
- Compare `UserIdentityTokens` as an unordered multiset instead of
requiring the server to preserve the original token enumeration order.
- Extend the client session test scaffolding so discovery endpoints can
be supplied explicitly.
- Add regression tests that verify `OpenAsync()` accepts reordered
`ServerEndpoints` and reordered `UserIdentityTokens`.
# Description
Fail reverse-connect listener startup immediately instead of logging
bind failures and surfacing a later connection timeout.
- Validate and stage configured and programmatic listener endpoints
before replacing active configuration.
- Open all listeners atomically and report endpoint-specific failures
with `BadTcpEndpointUrlInvalid`, the transport-specific status, or
`BadNoCommunication`.
- Roll back listeners opened by a failed attempt without reacquiring the
manager lock, including forced listener disposal when normal close
fails.
- Preserve meaningful `ServiceResultException` status codes through both
`StartService` overloads.
- Dispose replaced configuration watchers and reject callbacks from
stale watcher generations.
- Keep the intended shared-listener behavior: one long-lived
`ReverseConnectManager` can accept connections from multiple Servers on
the same Client URL.
- Expand `Docs/ReverseConnect.md` with listener lifetime, shared-manager
usage, diagnostics, and specification references.
## Validation
- `ReverseConnectManagerTests`: net10.0 and net48.
- `ReverseConnectHostTests`: net10.0 and net48.
- Ordered reverse-connect listener reuse integration tests: net10.0.
## Related Issues
- Relates to #3985.
## Checklist
- [ ] I have signed the
[CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf)
and read the
[CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md)
doc.
- [x] I have added tests that prove my fix is effective or that my
feature works and increased code coverage.
- [x] I have added all necessary documentation.
- [x] I have verified that my changes do not introduce (new) build or
analyzer warnings.
- [ ] I ran **all** tests locally using the **UA.slnx** solution against
at least .net **framework** and .net **10**, and all passed.
- [ ] I fixed **all** failing and flaky tests in the CI pipelines and
**all** CodeQL warnings.
- [ ] I have addressed **all** PR feedback received.
MrAlaskan