⚡ Simpler, faster msg-att parser (for fetch responses)

[nevans]

• Similar to ⚡ Simpler, faster response-data parser #201, but for msg-att.
• Converted the case statement to (mostly) use upcase'd strings, not regexps.
• The case stmt clauses were sorted. This might help with speed (need better msg-att frequency statistics to back up that claim) but it should definitely help to help avoid conflicts.
  • first the most commonly seen ones (UID and FLAGS),
  • then the ones in both 3051 and 9051 (sorted alphabetically),
  • then the ones in 3051 that were removed from 9051,
  • then MODSEQ (currently, the only supported attribute that's in neither 3501 or 9051).
• Rewrite the parser for section, section-spec, header-list, header-fld-name.
• Read the entire msg-att label for BODY[...]<...> prior to the case stmt. This greatly simplifies the code for reading attribute values, allowing much of it to be deleted.

I have written support for several more fetch msg-att, that builds on the changes in this PR:

• ✨ Add fetch support for BINARY and BINARY.SIZE #207 (BINARY and BINARY.SIZE) -- also needed for IMAP4rev2
• ✨ Add fetch support for EMAILID and THREADID #206 (for the OBJECTID extension)
• ✨ Add fetch support for Gmail's X-GM-EXT-1 extensions #209 X-GM-MSGID, X-GM-THRID, X-GM-LABELS (nonstandard GMail extensions)
• ANNOTATION
• PREVIEW
• SAVEDATE

[nevans]

I ran rake benchmarks:compare (see #208) on my phone (no YJIT). At least in this benchmark run and with the fetch examples I ran, they ranged from 1.02x faster to ~1.7x faster. None were slower than the v0.4.2 released version. The results:

$ rake benchmarks:compare BENCHMARK_ARGS="--filter 'fetch|FETCH|body|envelope'"
...
Comparison:
  bodystructure_bug11128_ext_mpart_without_lang
    v0.4.2-23-gef38f8e3:      3872.5 i/s
                  0.4.2:      3781.4 i/s - 1.02x  slower

  bodystructure_bug7146_msg_delivery_status
    v0.4.2-23-gef38f8e3:     18343.7 i/s
                  0.4.2:     16248.6 i/s - 1.13x  slower

  bodystructure_bug7147_message_rfc822_attachment
    v0.4.2-23-gef38f8e3:      6003.1 i/s
                  0.4.2:      5812.1 i/s - 1.03x  slower

  bodystructure_bug8167_delivery_status_with_extra_data
    v0.4.2-23-gef38f8e3:      4405.9 i/s
                  0.4.2:      4043.6 i/s - 1.09x  slower

  bodystructure_extension_fields
    v0.4.2-23-gef38f8e3:      2451.9 i/s
                  0.4.2:         0.0 i/s

  bodystructure_mixed_boundary
    v0.4.2-23-gef38f8e3:      2904.4 i/s
                  0.4.2:      2827.5 i/s - 1.03x  slower

  fetch_msg_att_flags_and_uid
    v0.4.2-23-gef38f8e3:     39067.9 i/s
                  0.4.2:     27161.4 i/s - 1.44x  slower

  fetch_msg_att_modseq
    v0.4.2-23-gef38f8e3:     36117.9 i/s
                  0.4.2:     21175.1 i/s - 1.71x  slower

  fetch_msg_att_rfc822
    v0.4.2-23-gef38f8e3:     54282.0 i/s
                  0.4.2:     38826.3 i/s - 1.40x  slower

  fetch_msg_att_uid
    v0.4.2-23-gef38f8e3:     57431.3 i/s
                  0.4.2:     39290.6 i/s - 1.46x  slower

  invalid_bodystructure_bug7153_mixed
    v0.4.2-23-gef38f8e3:     38287.5 i/s
                  0.4.2:     26330.9 i/s - 1.45x  slower

  invalid_bodystructure_message_sent_as_basic
    v0.4.2-23-gef38f8e3:      3738.5 i/s
                  0.4.2:      3533.7 i/s - 1.06x  slower

  invalid_fetch_msg_att_extra_space
    v0.4.2-23-gef38f8e3:     55393.5 i/s
                  0.4.2:     37536.6 i/s - 1.48x  slower

  invalid_fetch_msg_att_rfc822_with_brackets
    v0.4.2-23-gef38f8e3:     54756.6 i/s
                  0.4.2:     34460.4 i/s - 1.59x  slower

  rfc3501_7.4.2_FETCH_response_example
    v0.4.2-23-gef38f8e3:     43089.8 i/s
                  0.4.2:     28683.5 i/s - 1.50x  slower

  rfc3501_8_example_3_FETCH_ENVELOPE
    v0.4.2-23-gef38f8e3:      4197.2 i/s
                  0.4.2:      3762.7 i/s - 1.12x  slower

  rfc3501_8_example_4_FETCH_BODY[HEADER]
    v0.4.2-23-gef38f8e3:     41381.8 i/s
                  0.4.2:     30450.6 i/s - 1.36x  slower