Strengthen test ownership and RowBinary boundary safety

[ruslandoga]

Summary

• add wide SELECT and RowBinary INSERT matrices for heterogeneous composition coverage
• move exhaustive integer, decimal, string, and connection contracts to focused owner modules
• split incremental RowBinary decoding into independent async modules
• add adversarial boundary and property tests derived from each fixed-width encoder
• validate values before bitstring construction so overflow cannot silently wrap
• escape and parse hostile Enum labels losslessly

Corruption and robustness fixes

The new tests exposed and fix several cases beyond the originally reported Decimal issue:

• Decimal32/64/128/256 coefficients could wrap at their signed storage width
• scaling and rounding could introduce unchecked Decimal overflow
• declared Decimal precision and scale were not enforced for RowBinary
• non-finite Decimals raised incidental arithmetic errors
• Float32 overflow encoded infinity, which decoded as nil
• Date and DateTime values wrapped their UInt16/UInt32 storage
• DateTime64 ticks could overflow Int64
• IPv6 segments silently truncated; invalid IPv4 octets returned invalid iodata
• Enum labels containing quotes, backslashes, delimiters, controls, or NUL were not escaped or decoded correctly
• invalid/duplicate Enum mappings and invalid Decimal definitions were accepted

Adversarial coverage

• generated signed bit patterns for every Decimal storage width
• min/max and one-past-boundary cases
• scaling, rounding, precision, exponent, and non-finite Decimal cases
• Float32/Float64 overflow cases
• Date, DateTime, and DateTime64 storage boundaries
• generated IPv4 octets and every IPv6 segment bit pattern
• generated Enum type round-trips with quotes, backslashes, punctuation, whitespace, control bytes, Unicode, and NUL
• live ClickHouse Enum insert/select through escaped RowBinary type headers

Testing

• MIX_ENV=test mix format --check-formatted
• MIX_ENV=test mix compile --warnings-as-errors
• git diff --check
• MIX_ENV=test mix test --include slow --max-cases 8

Result: 484 passed (171 doctests, 37 properties, 276 tests).