feat: add SFTP file transfer and std::fs-compatible operations (#4)

* fix: correct spelling errors

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* fix: improve error handling for SSH connection timeout

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add file transfer capabilities via SFTP

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add `std::fs`-compatible file operations

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add test cases for file operations

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* docs: add README and update package metadata

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* fix: enhance symlink support and improve error handling

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

---------

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

Author: jjl9807

Cargo.lock

@@ -1,7 +1,15 @@
 [package]
 name = "qlean"
 version = "0.1.0"
+authors = ["jl.jiang <jiangjl9807@gmail.com>"]
+categories = ["development-tools::testing", "virtualization"]
+description = "A system-level isolation testing library based on QEMU/KVM."
+documentation = "https://docs.rs/qlean"
 edition = "2024"
+keywords = ["isolation", "testing", "kvm", "qemu"]
+license = "MIT"
+readme = "README.md"
+repository = "https://github.com/buck2hub/qlean"
 
 [dependencies]
 anyhow = "1.0.100"
@@ -12,6 +20,7 @@ futures = "0.3"
 nanoid = "0.4.0"
 reqwest = { version = "0.13.1", features = ["stream"] }
 russh = "0.55.0"
+russh-sftp = "2.1.1"
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.148"
 serde_yml = "0.0.12"
@@ -25,4 +34,5 @@ tracing = { version = "0.1.43", features = ["log"] }
 walkdir = "2.5.0"
 
 [dev-dependencies]
+tempfile = "3.24.0"
 tracing-subscriber = { version = "0.3.22", features = ["env-filter", "local-time"] }