Release 0.2.0: fallible numeric conversions and chained-expression fixes

[davassi]

Summary

Release 0.2.0. Makes numeric conversions fallible instead of panicking, fixes chained-expression handling, and grows the test suite from 36 to 64 tests.

Breaking change

From<Number> for i32/i64/i128/f64 panicked on out-of-range or non-finite values. It is replaced by TryFrom<Number>, which returns a ConversionError. Callers doing i64::from(n) must move to i64::try_from(n)?.

From<Number> for BigInt is kept but is now exact: it truncates the rational toward zero instead of round-tripping through f64, so large values no longer lose precision.

Fixes

• A trailing ; reported a spurious malformed-expression error after the assignment side-effect had already been applied. Chained expressions now return the last segment's value, and genuinely malformed segments are rejected.
• Removed the unused BitXor implementation for Number, which panicked internally.

Tests

36 → 64 tests, covering fallible/exact conversions, rounding on negatives, power edge cases, domain errors, variable case-insensitivity, chained assignment, square/mixed brackets, whitespace handling, decimal-literal parsing, and the Number Display / ConversionError messages.

Verification

cargo test passes locally: 28 integration tests, 31 unit tests, 5 doc-tests, 0 failures.

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Summary by cubic

Release 0.2.0 makes numeric conversions from Number fallible and fixes ;-chained expressions to return the last segment’s value. It also removes a panicking BitXor and expands test coverage.

• Migration

  • Replace into() calls with try_into()/TryFrom and handle ConversionError (e.g. let x: i64 = n.try_into()?;) for i32, i64, i128, and f64.
  • From<Number> for BigInt stays, and is now exact: it truncates toward zero without an f64 round-trip.

• Bug Fixes

  • Chained expressions: trailing ; returns the last segment’s value; malformed segments now error; assignment side-effects and reported values are consistent.
  • Removed an unused BitXor on Number that could panic.

^{Written for commit d4e035d. Summary will update on new commits.}