Fix Presto LOG(b, x) argument order on round-trip [CLAUDE]

[chuenchen309]

Presto's LOG(b, x) is the logarithm of x to base b, but round-tripping it through the Presto dialect silently swaps the two arguments: LOG(3, 9) (log base 3 of 9, = 2) comes back out as LOG(9, 3) (= 0.5). The SQL still looks valid, so the wrong value is easy to miss.

The cause is an inconsistency around the tri-state LOG_BASE_FIRST flag. Presto leaves it None; the parser treated None as falsy and swapped the arguments, while the generator only swaps when the flag is explicitly False. Changing the parser's check to is False matches the generator, so None dialects no longer swap. Base-first (True) and value-first (False) dialects are unaffected, and LOG2/LOG10 still transpile as before.

Verified against the full unit suite (1243 tests pass) and added a Presto round-trip test that fails without the change.

Disclosure: this change was found, fixed, tested and described by an AI agent (Claude Code) running on this account. The account holder reviews every change and is accountable for it.

[geooo109]

This is invalid in presto:

presto> SELECT LOG(2,8);

Query 20260720_104252_00010_i6tgb, FAILED, 0 nodes
Splits: 0 total, 0 done (0.00%)
[Latency: client-side: 16ms, server-side: 2ms] [0 rows, 0B] [0 rows/s, 0B/s]

Query 20260720_104252_00010_i6tgb failed: line 1:8: Function log not registered
SELECT LOG(2,8)

In trino (it's supported + the roundtrip is correct):

INPUT:
SELECT LOG(b, x)

AST:
Select(
  expressions=[
    Log(
      this=Column(
        this=Identifier(this=b, quoted=False)),
      expression=Column(
        this=Identifier(this=x, quoted=False)))])
SELECT LOG(b, x)

On the engine (trino):
trino> SELECT LOG(2,8);
 _col0 
-------
   3.0 
(1 row)

Query 20260720_104653_00001_q59b3, FINISHED, 1 node
Splits: 1 total, 1 done (100.00%)
0.13 [0 rows, 0B] [0 rows/s, 0B/s]

[georgesittas]

Assuming garbage in -> garbage out, this PR changes nothing:

1. The branch in build_logarithm only runs when a 2-arg LOG is parsed in a LOG_BASE_FIRST = None dialect.
2. The only None dialects are Presto and ClickHouse, and both engines reject 2-arg LOG

Therefore, every input whose behavior the PR changes is garbage.