Optimize Rust release binary size

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• Add size-focused release profile settings for the Rust workspace: symbol stripping, LTO, single codegen unit, opt-level = "z", and aborting panics
• Disable jsonschema's unused HTTP resolver and remove the unused CLI reqwest dependency
• Remove reqwest's JSON feature from pinget-core by using existing serde_json serialization/parsing in REST paths

Size impact

• Baseline cargo build -q -p pinget-cli --manifest-path rust\Cargo.toml --release: 28,922,368 bytes (27.58 MiB)
• Optimized release build: 11,576,320 bytes (11.04 MiB)
• Reduction: 17,346,048 bytes (16.54 MiB), about 60% smaller

Validation

• cargo +nightly fmt --manifest-path rust\Cargo.toml --all
• cargo clippy -q --manifest-path rust\Cargo.toml --workspace --tests -- -D warnings
• cargo test -p pinget-core --manifest-path rust\Cargo.toml
• cargo test -p pinget-cli --manifest-path rust\Cargo.toml
• cargo build -q -p pinget-cli --manifest-path rust\Cargo.toml --release