fix(connectors): encode FlatBuffer payloads using BFBS schemas

[Standing-Man]

Which issue does this PR address?

Relates to #3430.

Rationale

What changed?

Local Execution

• Passed / not passed
  Passed
• Pre-commit hooks ran / not ran
  Ran

AI Usage

[codecov]

Codecov Report

❌ Patch coverage is 85.69528% with 215 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.95%. Comparing base (a5001d3) to head (05cdf14).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
core/connectors/sdk/src/flatbuffer/schema.rs	79.85%	172 Missing and 24 partials ⚠️
core/connectors/sdk/src/structured.rs	96.09%	3 Missing and 8 partials ⚠️
core/connectors/sdk/src/encoders/flatbuffer.rs	96.77%	3 Missing and 5 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3734       +/-   ##
=============================================
- Coverage     74.34%   51.95%   -22.39%     
  Complexity      950      950               
=============================================
  Files          1303     1304        +1     
  Lines        148712   132787    -15925     
  Branches     124225   108373    -15852     
=============================================
- Hits         110562    68993    -41569     
- Misses        34673    60748    +26075     
+ Partials       3477     3046      -431     

Components	Coverage Δ
Rust Core	46.92% <85.69%> (-27.66%)	⬇️
Java SDK	62.64% <ø> (ø)
C# SDK	71.14% <ø> (-1.14%)	⬇️
Python SDK	92.27% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	92.69% <ø> (-0.02%)	⬇️
Go SDK	43.08% <ø> (ø)

Files with missing lines	Coverage Δ
core/connectors/sdk/src/lib.rs	56.17% <ø> (ø)
core/connectors/sdk/src/encoders/flatbuffer.rs	97.43% <96.77%> (+16.77%)	⬆️
core/connectors/sdk/src/structured.rs	96.09% <96.09%> (ø)
core/connectors/sdk/src/flatbuffer/schema.rs	79.85% <79.85%> (ø)

... and 386 files with indirect coverage changes

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