fix(number): allow float prefixes before non-exponent text

[sb123sb123]

Fixes #1725

Cause

The optional exponent parser uses cut(digit1) after consuming e or E. When that character starts ordinary trailing text, as in 123episode, the digit parser returns a fatal error instead of allowing the optional exponent to be skipped. The valid prefix 123 is therefore rejected.

Fix

Keep the cut behavior when an exponent reaches end-of-input, preserving the existing malformed/incomplete exponent behavior. When non-digit trailing input follows e or E, let the optional exponent backtrack. Apply the same parser change to complete, streaming, and mode-generic float recognizers.

Validation

• cargo +nightly test --offline -p nom — passed (208 library tests; all package integration tests and doctests passed).
• cargo +nightly test --offline -p nom --no-default-features — passed (324 doctests).
• cargo +nightly test --offline -p nom --no-default-features --features alloc — passed (324 doctests).
• cargo +nightly test --offline -p nom --features std — passed (324 doctests).
• cargo +nightly test --offline -p nom --no-default-features --features alloc,std — passed (324 doctests).
• cargo +nightly build --offline -p nom and the minimal alloc,std build — passed.
• cargo +nightly fmt --all -- --check — passed.
• cargo +nightly bench --offline --features "" — passed.
• The standalone regression reproducer now returns Ok(("episode", "123")); the same reproducer on the base commit returned Err(Failure(... code: Digit)).
• Stable focused checks before the host's stable Cargo component became unavailable: cargo test --offline --lib float_test (3 passed) and cargo test --offline --test float (6 passed).

Baseline limitations

The exact workspace test and documentation commands cannot complete on this Windows host because the unrelated benchmarks member's jemalloc-sys build reports “C compiler cannot create executables” (exit 77). Package documentation with RUSTDOCFLAGS=-D warnings also encounters existing rustdoc::redundant-explicit-links warnings in src/combinator/mod.rs. Beta and 1.65 toolchains were not installed, and stable Cargo was removed by a concurrent host job after the focused checks. These limitations are unrelated to this patch.

AI assistance disclosure

This PR was developed with autonomous GPT-5.6 assistance. Issue triage, reproduction, implementation, validation, diff inspection, commit signing, and submission were performed by the agent in the remote workspace.