Parse nonfinite numbers inside inline tables

[rupayon123]

Problem

toml.loads('t = {n = inf}') and the equivalent nan, +inf, and +nan inline values fail as invalid inline-table values, while the same numeric values parse in regular tables (#403). The inline-table gate also rejects a leading + on ordinary numbers.

Change

Let the inline gate pass the nonfinite spellings and positive numeric prefix through to the existing numeric parser. A parameterized regression checks the inline result against regular-table parsing for seven forms.

Validation

• New regression: 5 of 7 cases failed before the fix; all 7 pass afterward.
• pytest -q tests/test_api.py — 29 passed, 2 skipped.
• The seven cases agree with Python 3.12 tomllib.
• python3.12 -m compileall -q toml tests, git diff --check, and Flake8 on toml/decoder.py passed. Flake8 on the test file passed with E501 excluded; it has a pre-existing 84-character line at line 23.

A broad pytest -q collection attempt stopped on the existing stdin-based tests/encoding_test.py harness. No full conformance suite was run. Prepared with AI assistance.

Fixes #403.