refactor(connector): simplify pulsar reader

[shanicky]

Signed-off-by: Peng Chen peng@singularity-data.com

What's changed and what's your intention?

as title

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #3103 (350fb1a) into main (f5c62f8) will increase coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #3103      +/-   ##
==========================================
+ Coverage   73.48%   73.50%   +0.02%     
==========================================
  Files         734      734              
  Lines      100207   100175      -32     
==========================================
  Hits        73633    73633              
+ Misses      26574    26542      -32     

Flag	Coverage Δ
rust	73.50% <0.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
src/connector/src/pulsar/source/reader.rs	0.00% <0.00%> (ø)

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[tabVersion]

LGTM

lets fix pulsar client later