Chg #960: Pass non-null and non-expression values only to dbTypecast()

[KalimeroMK]

Fix #960

Changes

• null values are now passed through without calling ColumnInterface::dbTypecast(). The check is inlined at the call sites in AbstractDMLQueryBuilder (insert/update/batch) and AbstractColumnDefinitionBuilder::buildDefault().

• No new API. The first version of this PR added a dbTypecast() wrapper function, but a wrapper that only filters null adds call overhead for no measurable gain (see benchmark), so the check was inlined instead.

• DateTimeValueBuilder is untouched: DateTimeValue::$value is non-nullable by type.

• Column implementations are intentionally left untouched. Two findings from the driver test matrices:

  • Expression is Stringable, so removing the ExpressionInterface arms silently stringifies expressions instead of passing them through (breaks DDL builders in db-pgsql/db-mssql that pass Expression default values directly).
  • Some driver implementations process expressions: Yiisoft\Db\Mssql\Column\BinaryColumn::dbTypecast() unwraps Param values into CONVERT(VARBINARY(MAX), ...) expressions, so expressions must keep reaching dbTypecast().

  Net effect: only null is safe to pre-filter. Simplifying the implementations needs a coordinated change across the driver packages and can be done as a follow-up for 3.0.

Benchmark

2M calls per round, median of 7 rounds, PHP 8.5 with OPcache + JIT (tracing), workload: 80% scalars, 10% null, 10% expressions, IntegerColumn + StringColumn:

approach	time per round
current master (direct call)	~34 ms
wrapper function (first version of this PR)	~42 ms
check inlined at the call site (this PR)	~34.5 ms

The inlined check is within noise of master; the wrapper function added ~4 ns per call on trivial casts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.62%. Comparing base (f0b0d2b) to head (82017d6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1197   +/-   ##
=========================================
  Coverage     98.62%   98.62%           
- Complexity     1645     1649    +4     
=========================================
  Files           120      120           
  Lines          4288     4289    +1     
=========================================
+ Hits           4229     4230    +1     
  Misses           59       59           

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[Tigrov]

But it seems the function that only checks for null doesn't make sense.

#960 (comment)

[KalimeroMK]

Agreed that a null-only wrapper doesn't pay for itself — dropped the function and inlined the null check at the call sites in 82017d6. Benchmark is at parity with master now.

[Tigrov]

I'd leave it as is and close the issue without changes. The PR found that Expression cannot be moved outside of the type caster of the column classes. We have custom type casts possible, and null can be handled as a special case as described in the comment #960 (comment)

[samdark]

Yes, I agree that in this case the repetition is unavoidable and is actually okay.

[samdark]

@KalimeroMK thank you for the pull request. It helped.