Schema evolution error when querying Parquet files with different schema versions

### Apache Iceberg Rust version

0.5.1 (latest version)

### Describe the bug

When querying an Iceberg table that has evolved its schema, iceberg-rust fails if some underlying Parquet files do not yet contain the newly added field(s). This violates the schema evolution contract in Iceberg, where missing fields should be treated as null. Instead, the reader returns a schema mismatch error.

Error: External(DataInvalid => Parquet schema table {
1: t_id: optional string
2: primal_country: optional string
3: other_countries: optional string
4: primary_country_iso2: optional string
5: other_countries_iso2: optional string
}
and Iceberg schema table {
1: t_id: optional string
2: primal_country: optional string
3: other_countries: optional string
4: primary_country_iso2: optional string
5: other_countries_iso2: optional string
6: event_time: optional timestamp
}
do not match.

i was looking through the slack and found this - https://github.com/apache/iceberg-rust/pull/602 but im not sure this pr addresses this issue

### To Reproduce

1. spark.sql("""
CREATE OR REPLACE TABLE my_namespace.demo (
t_id BIGINT,
primal_country STRING,
other_countries STRING,
primary_country_iso2 STRING,
other_countries_iso2 STRING,
event_time TIMESTAMP
)
USING iceberg
""");
2. spark.sql("""
INSERT INTO demo (t_id, primal_country, other_countries, primary_country_iso2, other_countries_iso2)
VALUES
(1, 'USA', 'Canada,Mexico', 'US', 'CA,MX'),
(2, 'Germany', 'France,Italy', 'DE', 'FR,IT')
""")

3. Now modify the table schema
spark.sql("""ALTER TABLE demo
ADD COLUMNS (
event_time timestamp
)""")

4. Insert rows WITH event_time (evolved schema)
spark.sql("""
INSERT INTO demo (t_id, primal_country, other_countries, primary_country_iso2, other_countries_iso2, event_time)
VALUES
(3, 'India', 'Nepal,Bangladesh', 'IN', 'NP,BD', current_timestamp()),
(4, 'UK', 'Ireland,Scotland', 'GB', 'IE,SCT', current_timestamp())
""")

and now query the table using iceberg-rust - in my case i am working with aws-glue so i dont have a rust example to showcase

### Expected behavior

The query should succeed, returning results from both the old and new Parquet files. Files that don't contain the newly added ingest_ts field should have null or default values for it. This behavior is consistent with how schema evolution is handled in Iceberg (and in other implementations like Java or Python).

### Willingness to contribute

I would be willing to contribute a fix for this bug with guidance from the Iceberg community

Start by reproducing the issue with the Spark schema-evolution steps in the report, then trace the Parquet and Iceberg schema validation path in iceberg-rust. Done means querying the table succeeds across old and new Parquet files, with the newly added event_time field represented as null for older files.

Written by the indexing model from the issue text.