cubeapi: fix paused state parsing in sandbox list

[YangYuS8]

Summary

• Fix CubeAPI list status parsing for CubeMaster/Cubelet container state values.
• Return paused for list entries whose CubeMaster status is CONTAINER_PAUSED (5).
• Add a focused regression test for numeric and string paused list status values.

Fixes #218

Tests

• cargo fmt --check
• cargo +stable test
• cargo +stable clippy --all-targets --all-features
• Local HTTP verification with CubeAPI against a mock CubeMaster:
  • GET /sandboxes returns state: paused
  • GET /sandboxes/{id} still returns state: paused
  • GET /v2/sandboxes?state=paused returns the paused sandbox

Note: repo rust-toolchain 1.85.1 cannot run the current lockfile locally because time@0.3.47 requires rustc 1.88+.