fix: add http:// prefix to server address in schema requests

[raled573343]

Purpose of the PR

• Related to [Bug] Vermeer load task fails with "unable to connect" due to missing http:// in URL; after fix, Cardinality code 0 deserialization error #361 (partial fix)

This PR addresses the first issue described in #361: missing http:// prefix in schema request URLs. The PD service returns addresses as host:port without a scheme, causing HTTP client failures. This change adds the required prefix.

The second issue (Can't construct Cardinality from code 0) is a separate problem on the Store side and is not resolved by this PR. It should be handled in a separate fix.

Main Changes

• In vermeer/apps/common/hugegraph_tools.go:
  • Updated testServerIsValid: URL construction now uses "http://%v/graphspaces/...".
  • Updated GetHugegraphSchema: URL construction now uses "http://%v/graphspaces/...".

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests, such as (please modify tests here).
• Need tests and can be verified as follows.

Manual verification: after the fix, schema endpoint responds with HTTP 200.

Does this PR potentially affect the following parts?

• Nope
• Dependencies (add/update license info)
• Modify configurations
• The public API
• Other affects (typed here)

Documentation Status

• Doc - No Need

[imbajin]

Blocking: yes. Summary: Schema discovery can pass while HugeGraph write-back still fails because the discovered address remains scheme-less. Evidence: the exact-head flow stores the return value of FindServerAddr in output.hugegraph_server, and HugegraphWriter concatenates it into write-back URLs; the new prefix is applied only to the probe and schema read.

[imbajin]

⚠️ This prefixes only the request URL but returns the original addr. FindServerAddr() stores that value in output.hugegraph_server (vermeer/apps/worker/compute_bl.go:518), and HugegraphWriter.Init() concatenates it into request URLs at vermeer/apps/graphio/hugegraph.go:568,591,633. With PD returning server:8080, the probe now succeeds as http://server:8080/... but write-back constructs server:8080/graphspaces/..., which http.NewRequest rejects because it has no valid HTTP scheme. The same unconditional prefixing turns a pre-schemed address into http://http://... or http://https://..., whereas the old code accepted such a base URL. Normalize the address once at discovery, preserve an existing http/https scheme, use the normalized base for both read and write paths, and add raw and pre-schemed coverage.