Use `omitzero` JSON tag option for Qdrant request structs

[sim-wangyan]

Use omitzero JSON tag option for Qdrant request structs

Replace omitempty with omitzero (or add alongside) on Qdrant request struct fields, aligning with the Go 1.24 encoding/json best practice for distinguishing "unset" from "zero value" — without requiring pointer types for non-nil-able scalars.

Motivation

Introduced in Go 1.24, omitzero is a JSON struct tag option that omits a field when its value is the zero value for its type. Unlike omitempty, it correctly handles time.Time and makes intent explicit: the field should be omitted because the value is the default/unset state, not just "empty".

Currently, Qdrant request structs in to_qdrant_json.go use a mix of strategies:

Strategy	Example	Drawback
*float32 + omitempty	ScoreThreshold *float32 \json:"score_threshold,omitempty"``	Requires pointer allocation, GC pressure, extra nil-check
bool + omitempty	WithVector bool \json:"with_vector,omitempty"``	Works, but omitzero is semantically clearer
int + omitempty	HnswEf int \json:"hnsw_ef,omitempty"``	Same as above

This change does NOT affect the builder-layer pointer requirement (NilOrNumber, **float32 interface methods, condition filtering). The builder itself still needs pointers to distinguish "not provided" from "explicitly set to 0". This PR targets JSON serialization only.

Proposed Change

In to_qdrant_json.go, update the following struct fields:

1. Value-type fields: omitempty → omitzero

Struct	Field	Before	After
QdrantSearchParams	HnswEf	json:"hnsw_ef,omitempty"	json:"hnsw_ef,omitzero"
QdrantSearchParams	Exact	json:"exact,omitempty"	json:"exact,omitzero"
QdrantSearchParams	IndexedOnly	json:"indexed_only,omitempty"	json:"indexed_only,omitzero"
QdrantSearchRequest	WithVector	json:"with_vector,omitempty"	json:"with_vector,omitzero"
QdrantSearchRequest	Offset	json:"offset,omitempty"	json:"offset,omitzero"
QdrantRecommendRequest	WithVector	json:"with_vector,omitempty"	json:"with_vector,omitzero"
QdrantRecommendRequest	Offset	json:"offset,omitempty"	json:"offset,omitzero"
QdrantDiscoverRequest	WithVector	json:"with_vector,omitempty"	json:"with_vector,omitzero"
QdrantDiscoverRequest	Offset	json:"offset,omitempty"	json:"offset,omitzero"
QdrantScrollRequest	WithVector	json:"with_vector,omitempty"	json:"with_vector,omitzero"

2. Pointer-type fields: add omitzero alongside omitempty

Struct	Field	Before	After
QdrantSearchRequest	ScoreThreshold	json:"score_threshold,omitempty"	json:"score_threshold,omitempty,omitzero"
QdrantRecommendRequest	ScoreThreshold	json:"score_threshold,omitempty"	json:"score_threshold,omitempty,omitzero"
QdrantDiscoverRequest	ScoreThreshold	json:"score_threshold,omitempty"	json:"score_threshold,omitempty,omitzero"
QdrantRangeCondition	Gt, Gte, Lt, Lte	json:"...,omitempty"	json:"...,omitempty,omitzero"
All Qdrant request structs	Filter	json:"filter,omitempty"	json:"filter,omitempty,omitzero"
All Qdrant request structs	Params	json:"params,omitempty"	json:"params,omitempty,omitzero"

3. Unchanged fields

• WithPayload interface{} — not a scalar, stays omitempty
• Positive []int64, Negative []int64, Context []int64 — slices, stays omitempty
• Must []QdrantCondition, Should []QdrantCondition, MustNot []QdrantCondition — slices
• QdrantMatchCondition.Value interface{}, Any []interface{} — not scalars

Impact

• Breaking change: No. omitzero on bool/int behaves identically to omitempty. On pointer types, omitzero is additive and does not change behavior.
• Behavioral change: None. JSON output is unchanged for all existing inputs.
• Tests: All existing tests must continue passing (go test ./...).

Non-Goals

• This issue does NOT propose removing pointer types from the builder/condition layer.
• This issue does NOT propose changing the VectorDBRequest interface (GetScoreThreshold() **float32 etc.).
• This issue does NOT propose removing the nil_able.go helper functions.

Related

• Go 1.24 release notes (omitzero): https://go.dev/doc/go1.24#encoding/json
• Go 1.24+: omitzero is the recommended way to omit zero-valued fields