feat(bigtable): introduce PartialResultSetSource

[mpeddada1]

This PR introduces the PartialResultSetSource class. For processing data, the logic in the PR follows the pattern established by https://github.com/googleapis/googleapis/blob/4b1fe4dbb4156c42e9d09c294d74f36c7a3fc4ac/google/bigtable/v2/data.proto#L749-L770. Some things to note:

• Bigtable automatically sets the sentinel resume_token on the last batch of data read.
• The bigtable server also sends an error when the row size limit is reached (for reads).

Validation of the batch checksum will be done separately in a follow-up PR: #15617

[codecov]

Codecov Report

❌ Patch coverage is 91.45907% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.10%. Comparing base (393d5a9) to head (0d5d56c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...oud/bigtable/internal/partial_result_set_source.cc	79.24%	22 Missing ⚠️
...loud/bigtable/internal/partial_result_set_source.h	0.00%	2 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #15598 +/- ##
==========================================
- Coverage 93.11% 93.10% -0.01% 
==========================================
Files 2418 2424 +6 Lines 222977 223259 +282 ==========================================
+ Hits 207618 207865 +247 - Misses 15359 15394 +35 

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