refactor(schema): use REE field name constants

[akashchamp]

Closes #11035

Assisted-by: Codex

Summary

Use the existing REE default field-name constants wherever arrow-schema constructs fields with the default run_ends and values names. Intentional custom named_values parsing and display cases remain unchanged.

Testing

• cargo fmt --all -- --check
• cargo test -p arrow-schema — 108 unit tests and 41 doctests passed.
• cargo test -p arrow-schema --all-features — 179 unit tests and 43 doctests passed.
• cargo clippy -p arrow-schema --all-targets --all-features -- -D warnings
• Manually exercised display/parse round trips for both the default REE schema and a custom named_values schema; each parsed back to the original data type.

User-facing changes

None.

AI assistance was used to identify and apply the mechanical substitutions. I reviewed every changed construction and confirmed custom-name cases remain explicit.

[Rich-T-kid]

seems straightforward, thank you @akashchamp