feat(duckdb): Add transpilation support for CHR function.

[fivetran-amrutabhimsenayachit]

CHR with a float/decimal literal fails at runtime in DuckDB.
CHR(65.9) transpiles unchanged. Snowflake rounds 65.9 → 66 → 'B'; DuckDB strictly requires INTEGER and raises: No function matches the given name and argument types 'chr(DECIMAL(3, 1))'.

python -c "
from sqlglot import parse_one
from sqlglot.optimizer.annotate_types import annotate_types
expr = parse_one('SELECT CHR(65) AS chr_int, CHR(65.9) AS chr_float, CHAR(65) AS char_alias, CHR(NULL) AS chr_null, CHR(8364) AS chr_unicode', read='snowflake')
annotated = annotate_types(expr, dialect='snowflake')
print(annotated.sql('duckdb'))
"
-->
SELECT CHR(65) AS chr_int, CHR(CAST(65.9 AS INT)) AS chr_float, CHR(65) AS char_alias, CHR(NULL) AS chr_null, CHR(8364) AS chr_unicode

│ chr_int │ chr_float │ char_alias │ chr_null │ chr_unicode │
│ varchar │  varchar  │  varchar   │ varchar  │   varchar   │
├─────────┼───────────┼────────────┼──────────┼─────────────┤
│ A       │ B         │ A          │ NULL     │ €           │
└─────────┴───────────┴────────────┴──────────┴─────────────┘

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:RD-1147697-chr-char, sqlglot version: RD-1147697-chr-char)
• baseline (main, sqlglot version: 0.0.1.dev1)

By Dialect

dialect	main	sqlglot:RD-1147697-chr-char	transitions	links
bigquery -> bigquery	23872/23877 passed (100.0%)	21252/21252 passed (100.0%)	No change	full result / delta
bigquery -> duckdb	2106/2624 passed (80.3%)	0/0 passed (0.0%)	No change	full result / delta
duckdb -> duckdb	4003/4003 passed (100.0%)	4003/4003 passed (100.0%)	No change	full result / delta
snowflake -> duckdb	1511/2674 passed (56.5%)	0/0 passed (0.0%)	No change	full result / delta
snowflake -> snowflake	65910/65910 passed (100.0%)	63015/63015 passed (100.0%)	No change	full result / delta
databricks -> databricks	1364/1364 passed (100.0%)	1364/1364 passed (100.0%)	No change	full result / delta
postgres -> postgres	6040/6040 passed (100.0%)	6040/6040 passed (100.0%)	No change	full result / delta
redshift -> redshift	7059/7059 passed (100.0%)	7059/7059 passed (100.0%)	No change	full result / delta

Overall

main: 113551 total, 111865 passed (pass rate: 98.5%), sqlglot version: 0.0.1.dev1

sqlglot:RD-1147697-chr-char: 102733 total, 102733 passed (pass rate: 100.0%), sqlglot version: RD-1147697-chr-char

Transitions:
No change

✅ 4 test(s) passed