chore(build): tune release profile and QR dependency (#6660)

Switch IAM QR rendering from qrcode to qrcode-rs 2.0.0 while keeping only the std and svg feature path enabled.

Set the release profile to a single codegen unit and disable release debuginfo as requested.

Verification:

- cargo info qrcode-rs --registry crates-io

- cargo tree -p rustfs-iam -e features

- CARGO_TARGET_DIR=/private/tmp/rustfs-target-qrcode-rs-profile-tuning cargo test -p rustfs-iam --locked

- cargo fmt --all --check

- git diff --check

Co-authored-by: heihutu <heihutu@gmail.com>

Cargo.toml

@@ -291,7 +291,7 @@ percent-encoding = "2.3.2"
 # Server-side QR rendering for TOTP enrollment, so neither the console nor the
 # CLI needs its own QR encoder. No default features: the image/render backends
 # pull in an image stack this only needs SVG and text output from.
-qrcode = { version = "0.14.1", default-features = false, features = ["svg"] }
+qrcode-rs = { version = "2.0.0", default-features = false, features = ["std", "svg"] }
 pin-project-lite = "0.2.17"
 pretty_assertions = "1.4.1"
 rand = { version = "0.10.2" }
@@ -384,8 +384,8 @@ debug = "line-tables-only"
 [profile.release]
 opt-level = 3
 lto = "thin"
-codegen-units = 16
-debug = 2
+codegen-units = 1
+debug = 0
 strip = "symbols"
 split-debuginfo = "off"