Do StaleDnsHelper and the Aurora initial connection plugin stay inactive when the DSN uses a custom domain?

We reach an Aurora MySQL cluster through a custom domain, a CNAME pointing at the writer cluster endpoint, with `clusterInstanceHostPattern` set. During failover testing `StaleDnsHelper` never did anything. Pointing the DSN at the real cluster endpoint and changing nothing else made it active right away, and it logged several "Stale DNS data detected" reconnections.

Reading the source, that looks deliberate. Both checks look at the host string in the DSN:

- [`stale_dns_helper.go#L52`](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/awssql/plugins/stale_dns_helper.go#L52) returns the connection without verifying it unless `IsWriterClusterDns(host)` or `IsGlobalDbWriterClusterDns(host)`.
- [`aurora_initial_connection_strategy_plugin.go#L114-L115`](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/awssql/plugins/aurora_initial_connection_strategy_plugin.go#L114-L115) returns early unless `IdentifyRdsUrlType(hostInfo.GetHost()).IsRdsCluster`.

[`IsWriterClusterDns`](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/awssql/utils/rds_utils.go#L136) matches the host against the Aurora DNS regexes, which all require an AWS domain, so a custom domain cannot satisfy either check. Neither check uses `clusterInstanceHostPattern`. [`rds_host_list_provider.go#L103`](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/awssql/driver_infrastructure/rds_host_list_provider.go#L103) reads it only to build instance endpoints from topology rows.

Questions:

1. With `clusterInstanceHostPattern` set, does the wrapper support a custom domain in front of a cluster endpoint, or must the DSN use the cluster endpoint for the failover protections to run?
2. If it is a limitation, could the failover docs say so? [UsingTheBlueGreenPlugin.md](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/docs/user-guide/using-plugins/UsingTheBlueGreenPlugin.md#L21) says CNAME aliases are not supported, but only for Blue/Green, while [UsingTheFailoverPlugin.md](https://github.com/aws/aws-advanced-go-wrapper/blob/877b430/docs/user-guide/using-plugins/UsingTheFailoverPlugin.md#L30) describes `clusterInstanceHostPattern` as the parameter to use when connecting through a custom domain.
3. Is `utils.SetPreparedHostFunc` meant for user code? The only callers are the wrapper's own integration tests.

### The AWS Advanced Go Wrapper version used

`awssql/v2` v2.0.2, `mysql-driver` v1.1.2

### Go version used

go1.26.4 darwin/arm64

### Operating System and version

macOS 26.5 (arm64)

Start with awssql/plugins/stale_dns_helper.go, awssql/plugins/aurora_initial_connection_strategy_plugin.go, awssql/utils/rds_utils.go, and awssql/driver_infrastructure/rds_host_list_provider.go to trace the host checks and clusterInstanceHostPattern handling. Compare the behavior and wording in UsingTheFailoverPlugin.md and UsingTheBlueGreenPlugin.md. Done requires a maintainer decision on custom-domain support, with implementation or clarified documentation and relevant tests if the scope is accepted.

Written by the indexing model from the issue text.