feat(profile): emit Croissant descriptive statistics + frequency

[jqnatividad]

What

Stores qsv's per-column statistics and value-frequency distributions in the Croissant 1.1 projection of qsv profile, following the spec's Representing Descriptive Statistics application.

Statistics (via the spec's annotation mechanism)

• RecordSet-level row count, typed with Wikidata's Cardinality term (Q4049983), per the canonical person/count example.
• Per-Field annotation arrays of summary stats — min, max, mean, median, stddev, variance, range, sum, q1, q3, mode — each typed with its DDI-CDI SummaryStatisticType term (ddi-stats:*, verified against the live 2.1.2 vocabulary) as an sc:DefinedTerm. min/max also carry the schema.org equivalentProperty (sc:minValue / sc:maxValue) for numeric columns. Annotations are emitted only when qsv actually produced the stat (e.g. quartiles are null for text columns).

{
  "@id": "main-table/population/mean",
  "value": 5483333.3333,
  "dataType": {
    "@type": "sc:DefinedTerm",
    "termCode": "ArithmeticMean",
    "name": "Arithmetic mean",
    "@id": "ddi-stats:7975ed0",
    "inDefinedTermSet": "http://rdf-vocabulary.ddialliance.org/cv/SummaryStatisticType/2.1.2/"
  }
}

Frequency (opt-in via --croissant-frequency)

Croissant 1.1 has no canonical scalar slot for value distributions, so each column's top-N counts are emitted as a dedicated inline cr:RecordSet (<col>-frequency) of {value, count, percentage} rows — a first-class, queryable shape. Off by default to keep the projection compact; the raw counts always remain in the top-level frequency output block regardless of the flag.

Full extended stat set on a fresh run

The profile pipeline previously used the shared StatsMode::Schema (no median/quartiles/mode), so those only appeared when a richer --everything stats cache happened to exist. Added StatsMode::ProfileSchema (Schema + --quartiles --mode) and pointed the profile context builder at it. The schema command's lean Schema mode is untouched.

Other

• @context gains the ddi-stats prefix and an annotation term aliased to cr:annotation.
• Threads per-column frequency (dppf) into the projection context.
• Regenerated docs/help/profile.md.

Testing

• Updated croissant_emits_recordset_with_one_field_per_csv_column to assert the count annotation, per-field stat annotations, and frequency RecordSets (with --croissant-frequency).
• New croissant_frequency_off_by_default_extended_stats_on_fresh_run: verifies frequency is opt-in and median/quartiles/mode surface on a fresh run.
• cargo clippy -F all_features clean; cargo +nightly fmt --check clean.
• Tests pass: profile 62, schema 58, pivotp 62.

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[codacy-production]

Up to standards ✅

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[Copilot]

Pull request overview

Adds Croissant 1.1 descriptive-statistics output to qsv profile: per-RecordSet row count annotation, per-Field stat annotations (min/max/mean/median/stddev/variance/range/sum/q1/q3/mode) typed with DDI-CDI terms, and optional per-column value-frequency RecordSets behind a new --croissant-frequency flag. Also introduces a StatsMode::ProfileSchema variant so profile runs stats with --quartiles --mode and surfaces the extended stat set without a pre-built --everything cache.

Changes:

• New StatsMode::ProfileSchema (Schema + quartiles + mode) wired into profile's context builder.
• New --croissant-frequency flag threads dppf into the projection and emits inline <col>-frequency RecordSets; Croissant YAML template extended with annotation arrays and DDI-CDI/Wikidata typing.
• Test coverage updated/added for the new annotations and the opt-in frequency behaviour; help doc regenerated.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/util.rs	Adds ProfileSchema enum variant and its stats command construction.
src/cmd/profile/context.rs	Switches profile's schema-stats fetch to ProfileSchema.
src/cmd/profile.rs	Adds --croissant-frequency flag and threads frequency data into the projection context.
resources/profiles/croissant.yaml	Extends @context and recordset template with stat annotations and per-column frequency RecordSets.
docs/help/profile.md	Regenerated help to document the new flag.
tests/test_profile.rs	Updates existing assertion and adds a new test for opt-in behaviour and extended stats.