Added MarshalerSizer Interface to facilitate creation of Sizer implementations

[cpheps]

Description:
Proposing adding a new MarshalerSizer interface to ptrace, plog, and pmetric packages and alter NewProtoMarshaler to return this interface. This allows easy creation of a Sizer implementation. Currently the only way to create a sizer for the pdata packages is to call NewProtoMarshaler function then cast to a Sizer. This is not intuitive from an API standpoint that it should be safe to cast a Marshaler as a Sizer.

The MarshalerSizer interface is a combination of the Marshaler and Sizer interfaces.

If this is merged I will create a follow up PR to update the Batch Processor to use this rather than casting from a Marshaler.

Link to tracking Issue: #5920

Testing: Updated tests to use the MarshalSizer instead of casting.

[codecov]

Codecov Report

Merging #5929 (e9ddacb) into main (e0adb9d) will not change coverage.
The diff coverage is 100.00%.

❗ Current head e9ddacb differs from pull request most recent head 42e8441. Consider uploading reports for the commit 42e8441 to get more accurate results

@@           Coverage Diff           @@
##             main    #5929   +/-   ##
=======================================
  Coverage   91.80%   91.80%           
=======================================
  Files         198      198           
  Lines       12377    12377           
=======================================
  Hits        11363    11363           
  Misses        800      800           
  Partials      214      214           

Impacted Files	Coverage Δ
pdata/plog/pb.go	100.00% <100.00%> (ø)
pdata/pmetric/pb.go	100.00% <100.00%> (ø)
pdata/ptrace/pb.go	100.00% <100.00%> (ø)

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[codecov]

Codecov Report

Merging #5929 (e953488) into main (109c917) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5929   +/-   ##
=======================================
  Coverage   91.93%   91.93%           
=======================================
  Files         198      198           
  Lines       12417    12417           
=======================================
  Hits        11415    11415           
  Misses        791      791           
  Partials      211      211           

Impacted Files	Coverage Δ
pdata/plog/pb.go	100.00% <100.00%> (ø)
pdata/pmetric/pb.go	100.00% <100.00%> (ø)
pdata/ptrace/pb.go	100.00% <100.00%> (ø)

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[bogdandrutu]

I expect to remove some of the conversions to Sizer from batch processor, do I miss something and that is not possible?

[cpheps]

I expect to remove some of the conversions to Sizer from batch processor, do I miss something and that is not possible?

@bogdandrutu I wasn't sure if that should be part of this PR or not. This changes makes the current logic still valid. I was going to do a follow up PR with the batch processor changes but I can group them in here if you'd rather just have a single PR.

[bogdandrutu]

@cpheps sounds good, but still a question in the issue if you can respond