get schema with augmented/prefixed path

[shrey-gang]

With current implementation if we search for augment/prefixed path as below, the error was thrown in response.

./bin/schemac schema get --name srl --version 22.11.1 --vendor Nokia --path /network-instances/network-instance/protocols/protocol/srl_nokia-ospfv2:ospfv2

request:
path: {
  elem: {
    name: "network-instances"
  }
  elem: {
    name: "network-instance"
  }
  elem: {
    name: "protocols"
  }
  elem: {
    name: "protocol"
  }
  elem: {
    name: "srl_nokia-ospfv2:ospfv2"
  }
}
schema: {
  name: "srl"
  vendor: "Nokia"
  version: "22.11.1"
}

Error: rpc error: code = InvalidArgument desc = **unknown module prefix "srl_nokia-ospfv2"**

In-oder to search with augmented or prefixed path below changes are made, the breif description of the change

Added support for YANG augment paths in schema resolution. Enhanced getChildren() to include e.Augmented nodes alongside e.Dir children across all path traversal functions (expand.go, object.go, references.go, schema.go, container.go). Refactored persiststore.getSchema() to parse module prefixes (module:name) from path elements, validate first-element prefixes against root modules, and construct database keys using unprefixed names. Augmented modules in non-first path elements (e.g., srl_nokia-ospfv2:ospfv2) now resolve correctly without strict validation, enabling schema lookups for nodes introduced via YANG augment statements.

./bin/schemac schema get --name srl --version 22.11.1 --vendor Nokia --path /network-instances/network-instance/protocols/protocol/srl_nokia-ospfv2:ospfv2
request:
path: {
  elem: {
    name: "network-instances"
  }
  elem: {
    name: "network-instance"
  }
  elem: {
    name: "protocols"
  }
  elem: {
    name: "protocol"
  }
  elem: {
    name: "srl_nokia-ospfv2:ospfv2"
  }
}
schema: {
  name: "srl"
  vendor: "Nokia"
  version: "22.11.1"
}

response:
schema: {
  container: {
    name: "ospfv2"
    description: "Top-level configuration and operational state for\nOpen Shortest Path First (OSPF) v2"
    namespace: "http://openconfig.net/yang/network-instance"
    prefix: "oc-ospfv2"
    children: "areas"
    children: "global"
    module_name: "openconfig-ospfv2"
  }
}

[shrey-gang]

@steiler Please review this change.
I am unable to add reviewers or assignee to the PR, working on it.