Persist buffer size in the metadata

[SkymanOne]

Feat to #1869 and closes #1879

Adds "staticBufferSize" field to the metadata file:

Example:

      "maxEventTopics": 4,
      "staticBufferSize": 16384,
      "timestamp": {
        "displayName": [
          "Timestamp"
        ],
        "type": 11
      }

[codecov-commenter]

Codecov Report

Merging #1880 (7f012ed) into master (01f1cc6) will increase coverage by 0.04%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #1880      +/-   ##
==========================================
+ Coverage   53.00%   53.04%   +0.04%     
==========================================
  Files         212      212              
  Lines        6739     6745       +6     
==========================================
+ Hits         3572     3578       +6     
  Misses       3167     3167              

Files Changed	Coverage Δ
crates/ink/codegen/src/generator/metadata.rs	0.00% <0.00%> (ø)
crates/metadata/src/tests.rs	100.00% <ø> (ø)
crates/metadata/src/specs.rs	96.94% <100.00%> (+0.03%)	⬆️

... and 1 file with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more