Remove os.Exit callsites below the entrypoint: phase 2 (#2202)

* Remove os.Exit callsites below the entrypoint: phase 2 (plans/exit.md)

Phase 2 of plans/exit.md: the FlagParser signature change.

- FlagParser gains an error return; all 259 inline parser closures in
  option_parse.go and NoOpParse1 updated (mechanical rewrite, compiler-checked).
- FlagTable.Parse returns (bool, error); its nine callers (climain passes one
  and two, .mlrrc line handling, verb-local flag parsing in tee/join/put/
  filter/split, and the repl/script terminals) propagate the error instead of
  letting parsers kill the process.
- cli.CheckArgCount returns its missing-argument message as an error rather
  than printing and exiting; new cli.FlagErrorf (counterpart of VerbErrorf)
  carries user-facing main-flag messages.
- The 14 print-and-exit sites inside parser closures become returned errors;
  --list-color-codes/--list-color-names return ExitRequest{0} after printing.
- The repl and script terminals translate ExitRequest into their int return
  codes, so 'mlr repl --list-color-codes' still exits 0.
- pkg/cli is now os.Exit-free; stale comments about exiting parsers updated
  (the completion introspection accessors remain, since parsers mutate the
  options struct).

Stderr messages and exit codes are byte-identical, including the two-line
missing-argument and --seed messages and the trailing-period forms pinned by
test/cases/cli-mfrom/0003.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Merge main (recutils #2201); convert its three new parser closures

Same mechanical rewrite as the rest of phase 2: error return signature plus
final 'return nil' on --irecutils/--orecutils/--recutils.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

pkg/terminals/repl/entry.go

@@ -20,12 +20,14 @@
 package repl
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path"
 	"strings"
 
 	"github.com/johnkerl/miller/v6/pkg/cli"
+	"github.com/johnkerl/miller/v6/pkg/lib"
 )
 
 func replUsage(verbName string, o *os.File, exitCode int) {
@@ -140,7 +142,15 @@ func ReplMain(args []string) int {
 				argi += 1
 			}
 
-		} else if cli.FLAG_TABLE.Parse(args, argc, &argi, options) {
+		} else if handled, flagErr := cli.FLAG_TABLE.Parse(args, argc, &argi, options); flagErr != nil {
+			var exitRequest *lib.ExitRequest
+			if errors.As(flagErr, &exitRequest) {
+				return exitRequest.Code
+			}
+			fmt.Fprintf(os.Stderr, "%v\n", flagErr)
+			return 1
+
+		} else if handled {
 
 		} else {
 			replUsage(replName, os.Stderr, 1)