Find a Tender API client updates

- Convert OCDS releases to types.Opportunity (internal/types); FetchOnce
  and FetchAll now return opportunities, built from each ocid's latest
  release
- Include each item's main classification as well as its additional ones
- Return ErrUnexpectedStatus for non-200 responses and
  ErrRateLimitExceeded for a repeated 429; close discarded bodies
- Stop fetchAll on a repeated next link and close each page's body once
  read rather than deferring in the loop
- Default a zero Since to 24 hours ago
- Merge date repair and releaseIDs into api.go
- Filter --planning/--opportunities/--awards on each procedure's current
  stage, using OCDS release tags; --opportunities previously matched a
  nonexistent "opportunity" tag and returned nothing
- Reject conflicting filters before fetching (cobra flag group)

internal/types/classifications.go

@@ -0,0 +1,8 @@
+package types
+
+type ClassificationCode struct {
+	ID             int64  `db:"id"             json:"id"`
+	IsCPV          bool   `db:"is_cpv"         json:"is_cpv"`
+	Code           string `db:"code"           json:"code"`
+	Classification string `db:"classification" json:"classification"`
+}

internal/types/opportunities.go

@@ -0,0 +1,41 @@
+package types
+
+import (
+	"time"
+)
+
+type Opportunity struct {
+	UUID              string               `db:"uuid"                json:"uuid"`
+	UUIDType          string               `db:"uuid_type"           json:"uuid_type"`
+	Title             string               `db:"title"               json:"title"`
+	Status            string               `db:"status"              json:"status"`
+	Description       string               `db:"description"         json:"description"`
+	BuyerName         string               `db:"buyer_name"          json:"buyer_name"`
+	Classifications   []ClassificationCode `db:"-"                   json:"classifications"`
+	BuyerId           string               `db:"buyer_id"            json:"buyer_id"`
+	MainCategory      string               `db:"main_category"       json:"main_category"`
+	ProcurementMethod string               `db:"procurement_method"  json:"procurement_method"`
+	MultiLot          bool                 `db:"multi_lot"           json:"multi_lot"`
+	SMESuitable       bool                 `db:"sme_suitable"        json:"sme_suitable"`
+	VCSESuitable      bool                 `db:"vcse_suitable"       json:"vcse_suitable"`
+	StartDate         *time.Time           `db:"start_date"          json:"start_date"`
+	EndDate           *time.Time           `db:"end_date"            json:"end_date"`
+	GrossValue        float64              `db:"gross_value"         json:"gross_value"`
+	HasDocuments      bool                 `db:"has_documents"       json:"has_documents"`
+	LatestReleaseDate time.Time            `db:"latest_release_date" json:"latest_release_date"`
+	Releases          []OpportunityRelease `db:"-"                   json:"releases"`
+}
+
+type OpportunityRelease struct {
+	UUID        string                  `db:"uuid"         json:"uuid"`
+	ReleaseID   string                  `db:"release_id"   json:"release_id"`
+	ReleaseDate time.Time               `db:"release_date" json:"release_date"`
+	Tags        []OpportunityReleaseTag `db:"-"            json:"release_tags"`
+	JSON        string                  `db:"data"         json:"data"`
+}
+
+type OpportunityReleaseTag struct {
+	UUID      string `db:"uuid"       json:"uuid"`
+	ReleaseID string `db:"release_id" json:"release_id"`
+	Tag       string `db:"tag"        json:"tag"`
+}