Add comprehensive documentation, tests, and quality tooling

- Add comprehensive doc comments to all public functions, structs, and modules following RUST_STANDARDS.md format
- Add unit tests for models.rs (serialization, deserialization, response creation)
- Add unit tests for db.rs (key building, parsing, expiration checking)
- Fix clippy warnings (unused imports, dead code, large enum variant with Box<PricingData>)
- Add rustfmt.toml and clippy.toml configuration files
- Add check-quality.sh script for running all quality checks
- Add fix-quality.sh script for automatically fixing formatting and clippy issues
- Verify cargo doc generates clean documentation with no warnings
- 25 tests added (22 passing, 3 need JSON deserialization fixes)

Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

rustfmt.toml

@@ -0,0 +1,55 @@
+# Rust formatting configuration for crud-pricing
+#
+# This configures rustfmt for consistent code formatting across the project.
+# Run with: cargo fmt
+
+# Edition
+edition = "2021"
+
+# Maximum line width
+max_width = 100
+
+# Use tabs (false = spaces)
+hard_tabs = false
+
+# Tab width/spaces
+tab_spaces = 4
+
+# Newline style
+newline_style = "Unix"
+
+# Use field init shorthand if possible
+use_field_init_shorthand = true
+
+# Use try shorthand
+use_try_shorthand = true
+
+# Format string literals where necessary
+format_strings = true
+
+# Merge imports
+imports_granularity = "Crate"
+
+# Group imports
+group_imports = "StdExternalCrate"
+
+# Reorder imports
+reorder_imports = true
+
+# Reorder modules
+reorder_modules = true
+
+# Match block trailing comma
+match_block_trailing_comma = true
+
+# Wrap comments at max_width
+wrap_comments = true
+
+# Format doc comments
+format_code_in_doc_comments = true
+
+# Normalize doc attributes
+normalize_doc_attributes = true
+
+# Use small heuristics
+use_small_heuristics = "Default"