fix: better performance for labelled matrix display

[thofma]

Current master:

julia> t = character_table("B");  # if you really want to see the formatted output then omit the semicolon

julia> @time show(IOBuffer(), "text/plain", t);
  9.962639 seconds (74.39 M allocations: 4.077 GiB, 5.35% gc time, 76.55% compilation time)

julia> @time show(IOBuffer(), "text/plain", t);
  2.275388 seconds (20.78 M allocations: 1.275 GiB, 3.93% gc time)

With this PR:

julia> t = character_table("B");  # if you really want to see the formatted output then omit the semicolon

julia> @time show(IOBuffer(), "text/plain", t);
  2.590985 seconds (8.90 M allocations: 575.139 MiB, 10.43% gc time, 95.47% compilation time)

julia> @time show(IOBuffer(), "text/plain", t);
  0.130060 seconds (1.57 M allocations: 76.671 MiB)

[ThomasBreuer]

Nice, thanks.

[codecov]

Codecov Report

Merging #3602 (9376127) into master (24e629c) will increase coverage by 0.41%.
Report is 5 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3602      +/-   ##
==========================================
+ Coverage   81.75%   82.17%   +0.41%     
==========================================
  Files         573      573              
  Lines       77557    77621      +64     
==========================================
+ Hits        63407    63782     +375     
+ Misses      14150    13839     -311     

Files	Coverage Δ
src/Groups/MatrixDisplay.jl	98.36% <100.00%> (+<0.01%)	⬆️

... and 42 files with indirect coverage changes