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)

cmd/jobsearch/main.go

@@ -19,9 +19,8 @@ package main
 
 import (
 	"fmt"
-	"os"
-
 	"log/slog"
+	"os"
 	"strings"
 
 	"git.avsdev.uk/Go/job-search/internal/cli"