Guard date_trunc lower-bound truncation

[Sean-Kenneth-Doherty]

Which issue does this PR close?

• Closes panic: date_trunc unwraps out-of-range lower-bound timestamp truncation #22214.

Rationale for this change

Truncating a near-lower-bound nanosecond timestamp to a coarser calendar unit can produce a timestamp outside Arrow's nanosecond range. date_trunc_coarse already used fallible timestamp conversion, but it unwrapped the final conversion back to nanoseconds and could panic.

What changes are included in this PR?

• Convert the final out-of-range truncation case into a DataFusion execution error.
• Add a small string helper for user-facing granularity names in the error.
• Add a unit regression and a sqllogictest regression for lower-bound nanosecond truncation.

Are these changes tested?

Yes:

• cargo fmt --check
• git diff --check
• CARGO_TARGET_DIR=/home/sean/Projects/datafusion-runtime-set-nonascii/target CARGO_BUILD_JOBS=2 cargo test -p datafusion-functions --lib date_trunc_out_of_range_lower_bound_returns_error
• CARGO_TARGET_DIR=/home/sean/Projects/datafusion-runtime-set-nonascii/target CARGO_BUILD_JOBS=2 cargo test -p datafusion-sqllogictest --test sqllogictests -- date_trunc_boundaries.slt
• CARGO_TARGET_DIR=/home/sean/Projects/datafusion-runtime-set-nonascii/target CARGO_BUILD_JOBS=2 cargo clippy -p datafusion-functions --lib -- -D warnings

Are there any user-facing changes?

Instead of panicking, out-of-range date_trunc results now return an error.

[Sean-Kenneth-Doherty]

Local validation for the current head (40335934b):

• cargo fmt --check --all
• git diff --check origin/main...HEAD && git diff --check
• cargo test -p datafusion-functions date_trunc_out_of_range_lower_bound_returns_error (1 passed)
• Ran the locally built sqllogictests driver from datafusion/sqllogictest with the date_trunc_boundaries filter; it completed 1/1 files.

Hosted checks currently only show the labeler, so this covers the focused unit and SQL regression paths for the lower-bound date_trunc case.