feat: datetime expansion (#917)

### Description

Adds support for abbreviated datetime formats (year, year-month, date)
via a new `Search::normalize_datetimes()` method. This allows users to
opt-in to expanding partial dates to full RFC 3339 datetime ranges -
follows similar functionality to `pystac`.

**Key changes:**
- Implemented `expand_datetime_to_start()` and
`expand_datetime_to_end()` helper functions to convert abbreviated dates
to full datetime ranges
- Added `Search::normalize_datetimes()` method for opt-in datetime
normalization
- Added two new error variants: `InvalidYear` and
`UnrecognizedDateFormat` for better error handling
- Comprehensive documentation and test coverage

**Sidecar changes:**
Bumped assert_cmd from 2.0 to 2.1 in workspace dependencies. The locked
version (2.0.14) was missing the `cargo_bin_cmd!()` macro (see
[docs](https://docs.rs/assert_cmd/2.0.17/assert_cmd/cargo/)), causing
compilation failures in test code that relied on it

### Related issues

- Closes [#463](#463)

### Checklist

- [x] Unit tests
- [x] Documentation, including doctests
- [x] Pull request title follows [conventional
commits](https://www.conventionalcommits.org/en/v1.0.0/)
- [x] Pre-commit hooks pass (`prek run --all-files`)

Author: jjcfrancisco

Cargo.toml

@@ -39,7 +39,7 @@ arrow-cast = "56.0.0"
 arrow-json = "56.0.0"
 arrow-schema = "56.0.0"
 assert-json-diff = "2.0"
-assert_cmd = "2.0"
+assert_cmd = "2.1"
 async-recursion = "1.1.1"
 async-stream = "0.3.6"
 async-trait = "0.1.89"

crates/cli/src/lib.rs

@@ -382,6 +382,7 @@ impl Rustac {
                     items: get_items,
                 };
                 let search: Search = get_search.try_into()?;
+                let search = search.normalize_datetimes()?;
                 let item_collection = if use_duckdb {
                     stac_duckdb::search(href, search, *max_items)?
                 } else {