fix(#687): distinguish operation cancellation from query timeouts

[cofin]

Summary

• add OperationCancelledError as a sibling of QueryTimeoutError
• distinguish native cancellation from timeout and deadline signals across ADBC, DuckDB, SQLite, PostgreSQL, Oracle, BigQuery, and Spanner adapters
• treat bare PostgreSQL SQLSTATE 57014 as OperationalError unless native status or message evidence identifies the cause
• document the compatibility change and migration path

Root cause

The shared exception contract grouped explicit caller or operator cancellation with elapsed query timeouts. That lost native distinctions such as ADBC CANCELLED versus TIMEOUT and caused callers catching QueryTimeoutError to receive user-initiated cancellation as though a deadline had elapsed.

The shared message classifier now checks timeout markers first because server messages such as canceling statement due to statement timeout contain both cancellation and timeout language.

Closes #687

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.18919% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.41%. Comparing base (0adde96) to head (c5d0088).

Files with missing lines	Patch %	Lines
sqlspec/adapters/adbc/core.py	77.77%	4 Missing and 2 partials ⚠️
sqlspec/adapters/adbc/type_converter.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #689      +/-   ##
==========================================
+ Coverage   77.38%   77.41%   +0.03%     
==========================================
  Files         476      476              
  Lines       68211    68266      +55     
  Branches     9385     9403      +18     
==========================================
+ Hits        52782    52846      +64     
+ Misses      12022    12015       -7     
+ Partials     3407     3405       -2     

Flag	Coverage Δ
integration	60.87% <33.78%> (-0.04%)	⬇️
py3.10	75.72% <85.13%> (+0.02%)	⬆️
py3.11	64.74% <82.43%> (-10.97%)	⬇️
py3.12	75.73% <85.13%> (+0.02%)	⬆️
py3.13	75.74% <85.13%> (+0.03%)	⬆️
py3.14	76.61% <85.13%> (+0.03%)	⬆️
unit	65.04% <82.43%> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sqlspec/adapters/aiomysql/data_dictionary.py	53.10% <ø> (ø)
sqlspec/adapters/aiosqlite/core.py	80.85% <100.00%> (ø)
sqlspec/adapters/asyncmy/data_dictionary.py	53.10% <ø> (ø)
sqlspec/adapters/asyncpg/core.py	78.18% <100.00%> (+0.55%)	⬆️
sqlspec/adapters/asyncpg/data_dictionary.py	70.25% <ø> (ø)
sqlspec/adapters/bigquery/core.py	73.12% <100.00%> (+1.00%)	⬆️
sqlspec/adapters/bigquery/data_dictionary.py	54.66% <ø> (ø)
...spec/adapters/cockroach_asyncpg/data_dictionary.py	42.02% <ø> (ø)
...spec/adapters/cockroach_psycopg/data_dictionary.py	37.19% <ø> (ø)
sqlspec/adapters/duckdb/core.py	88.08% <100.00%> (+1.03%)	⬆️
... and 22 more

... and 1 file with indirect coverage changes

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