feat: Add support for ordering by multiple fields. (#57)

## What

Add a `TopDocs::order_by` method, which supports ordering by multiple fast fields and scores in one collection pass, as defined by the `TopOrderable` trait. The `TopOrderable` trait is implemented (by a macro) for tuples of length 1 through 3 (for now).

## How

Add:
* a `TopOrderable` trait which is implemented for tuples, and a `TopOrderableCollector` to collect for it.
* a `Feature` trait which is implemented for `Score`s, and for fast fields.
    * To allow for boxing/dynamic dispatch of `Features` (which reduces code generation when the sort columns are not known until runtime), `Arc<dyn Feature>` is implemented via `ErasedFeature`.  
* a `TopNCompare` trait which can be used together with a `LazyTopNComputer` to lazily fetch columns during TopN.
    * This new interface is necessary because `TopNComputer` does not allow for lazily fetching additional fields for the comparison tuple, which can eliminate a lot of IO when tiebreakers are only rarely actually coming into play in the comparison (because most values are being eliminated by earlier columns).
    * It could also allow for making `DocId`/`DocAddress` tiebreaking optional ([see](quickwit-oss#2672 (comment))), via something like a "`DocIdFeature`".

This interface additionally could not use the `CustomScorer` APIs because it does not allow segments to Top-N a different type than their final output type (which is essential for ordering by `String`s).

## Note

This patch isolates everything to one module, but should almost certainly be split up into multiple modules, and better integrated with the existing modules. I was hoping to get some feedback on it before rearranging things, but I'm very happy to do so!

----

Upstream at quickwit-oss#2681

Author: stuhood

Cargo.toml

@@ -60,6 +60,7 @@ itertools = "0.14.0"
 measure_time = "0.9.0"
 arc-swap = "1.5.0"
 bon = "3.3.1"
+paste = "1.0.11"
 
 columnar = { version = "0.6", path = "./columnar", package = "tantivy-columnar" }
 sstable = { version = "0.6", path = "./sstable", package = "tantivy-sstable", optional = true }
@@ -86,7 +87,6 @@ pretty_assertions = "1.2.1"
 proptest = "1.0.0"
 test-log = "0.2.10"
 futures = "0.3.21"
-paste = "1.0.11"
 more-asserts = "0.3.1"
 rand_distr = "0.4.3"
 time = { version = "0.3.10", features = ["serde-well-known", "macros"] }

src/collector/mod.rs

@@ -96,6 +96,9 @@ pub use self::multi_collector::{FruitHandle, MultiCollector, MultiFruit};
 
 mod top_collector;
 
+mod top_orderable;
+pub use self::top_orderable::{Feature, FieldFeature, ScoreFeature};
+
 mod top_score_collector;
 pub use self::top_collector::ComparableDoc;
 pub use self::top_score_collector::{TopDocs, TopNComputer};