cat-file: speed up default format

cat-file: speed up default format

eb54a3391b (cat-file: skip expanding default format, 2022-03-15) added
special handling for the default batch format.  In the meantime it has
fallen behind the code path for handling arbitrary formats.  Bring it up
to speed by using the new and more efficient strbuf_add_oid_hex() and
strbuf_add_uint() instead of strbuf_addf():

Benchmark 1: ./git_main cat-file --batch-all-objects --batch-check='%(objectname) %(objecttype) %(objectsize)'
  Time (mean ± σ):      1.051 s ±  0.003 s    [User: 1.027 s, System: 0.023 s]
  Range (min … max):    1.049 s …  1.058 s    10 runs

Benchmark 2: ./git_main cat-file --batch-all-objects --batch-check='%(objectname)-%(objecttype)-%(objectsize)'
  Time (mean ± σ):      1.012 s ±  0.002 s    [User: 0.988 s, System: 0.023 s]
  Range (min … max):    1.010 s …  1.018 s    10 runs

Benchmark 3: ./git cat-file --batch-all-objects --batch-check='%(objectname) %(objecttype) %(objectsize)'
  Time (mean ± σ):     979.0 ms ±   1.1 ms    [User: 954.1 ms, System: 23.2 ms]
  Range (min … max):   977.7 ms … 980.8 ms    10 runs

Summary
  ./git cat-file --batch-all-objects --batch-check='%(objectname) %(objecttype) %(objectsize)' ran
    1.03 ± 0.00 times faster than ./git_main cat-file --batch-all-objects --batch-check='%(objectname)-%(objecttype)-%(objectsize)'
    1.07 ± 0.00 times faster than ./git_main cat-file --batch-all-objects --batch-check='%(objectname) %(objecttype) %(objectsize)'

Signed-off-by: René Scharfe <redacted>
Signed-off-by: Junio C Hamano <redacted>