B::UNOP_AUX::string doesn't handle new multiparam op

[tonycoz]

Module: B

Description
The B module implements a string() method for core UNOP_AUX ops, producing an argument string that summarises the contents of the auxiliary vector.

There is no such handling for multiparam.

Steps to Reproduce
Most obvious in B::Concise output:

$ ./perl -Ilib -MO=Concise,f -e 'use v5.42.0; sub f($x) { }'
main::f:
4  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <1> ex-argcheck KP/1 ->4
-        <@> lineseq K ->-
1           <;> nextstate(main 5 -e:1) :us,*,&,$,fea=9,0x10 ->2
2           <+> multiparam() ->3
3           <;> nextstate(main 5 -e:1) :us,*,&,$,fea=9,0x10 ->4
-e syntax OK

Expected behavior
B::UNOP_AUX::string() should summarise the details of the OP.

Perl configuration

# perl -V output goes here
  Derived from: 7e7a0417e29b77e1b8c1eb2c950a71a6cc799f33
  Platform:
    osname=linux
    osvers=6.12.57+deb13-amd64
    archname=x86_64-linux
    uname='linux venus 6.12.57+deb13-amd64 #1 smp preempt_dynamic debian 6.12.57-1 (2025-11-05) x86_64 gnulinux '
    config_args='-des -Dusedevel -Doptimize=-O0 -ggdb3'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O0 -ggdb3'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='14.2.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/x86_64-linux-gnu /usr/lib /usr/lib64
    libs=-lpthread -lgdbm -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=/lib/x86_64-linux-gnu/libc.so.6
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.41'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O0 -ggdb3 -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_DEVEL
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Locally applied patches:
    uncommitted-changes
  Built under linux
  Compiled at Jan  8 2026 10:53:33
  %ENV:
    PERLBREW_BASHRC_VERSION="0.43"
    PERLBREW_HOME="/home/tony/.perlbrew"
    PERLBREW_MANPATH=""
    PERLBREW_PATH="/home/tony/perl5/perlbrew/bin"
    PERLBREW_ROOT="/home/tony/perl5/perlbrew"
    PERLBREW_VERSION="0.67"
  @INC:
    lib
    /usr/local/lib/perl5/site_perl/5.43.7/x86_64-linux
    /usr/local/lib/perl5/site_perl/5.43.7
    /usr/local/lib/perl5/5.43.7/x86_64-linux
    /usr/local/lib/perl5/5.43.7

[tonycoz]

@leonerd I don't know if you want to look at this, otherwise I will next week-ish (self-assigned so I don't forget)