(Calculated fields) Add calculated-field predicates to QueryAst

[fulmicoton]

Description

Add calculated-field predicates to Quickwit's native query AST and search preparation.

• Add QueryAst::CalcField(CalcFieldQuery) with a jitexpr expression serialized as a string, including visitor/transformer support and user-query parsing passthrough.
• Lower predicates directly to Tantivy's JitExprPredicate / DocPredicateQuery, keeping JIT compilation and execution in Tantivy.
• Collect referenced fast fields for warmup, including string dictionaries through the existing whole-column warmup path. Preserve exact field paths and skip cache-hit subtrees.
• Treat calculated predicates conservatively during tag pruning and retain required-term behavior for ordinary query clauses.
• Enable Tantivy's jitexpr feature and pin f1413a4dcfd1386a22df7d960a754b4bcfb1c3b4 (the tip of paul.masurel/jitexpr-docpredicate), including support for . and # in expression variable names. Update dependency licenses.
• Add focused tests and internal documentation. AST containers retain PartialEq but no longer implement Eq, matching jitexpr's expression type.

Example:

{
  "type": "calc_field",
  "expression": "(GT custom.duration 1i64)"
}

How was this PR tested?

• cargo nextest run -p quickwit-query --locked: 172 passed, including 12 CalcField tests.
• cargo nextest run -p quickwit-doc-mapper -E 'test(query_builder::) | test(tag_pruning::)' --locked: 28 passed.
• Formatting, license generation, and diff whitespace checks passed during implementation.
• The upstream parser change was tested with the jitexpr and Tantivy document-predicate suites before pushing it.

Draft follow-ups / known limitations

• cargo check --locked still fails at quickwit-directories/src/hot_directory.rs:462: the pinned Tantivy IndexMeta does not expose list_segment_files.
• A prior full doc-mapper test run hit the order-sensitive test_concatenate_multiple_field test with default features. A diagnostic run with serde_json/preserve_order passed; no test or feature workaround was applied.
• Add a full remote-storage root-to-leaf regression test.
• Calculated-field definitions, aggregation expressions, and Elasticsearch DSL syntax are outside this PR. Expression variables currently refer directly to fast fields.