reconstruct: try salt components alongside the intact reactant record

A logged reactant routinely bundles a spectator counterion with the reactive
species (K/Na trifluoroborate, amine.HCl, sodium alkoxide) in one container.
Handed the whole thing, the reactor faithfully carries the spectator into the
generated product, which can then never equal the salt-free target, so a real
match is lost.

Components are now offered as extra candidates *in addition to* the intact
container, never instead of it: the counterion is sometimes retained on both
sides (amine.HCl -> amine'.HCl) and that only reconstructs from the intact
form. The intact form is listed first and every phase returns on first
success, so records that already matched keep their exact result.
_mixes_views bars a subset from pairing a record with its own component, while
still allowing two components of one record (a co-formulated pair).

ELN corpus (17222 records): 785 -> 968 matched, no losses, no label changes,
no new errors; all 183 gained mappings validate as CGRs. Runtime unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

update: expand README features and optional extras

- Detailed compatibility table for toolkit APIs (RDKit, Open Babel, etc.).
- Added IUPAC name generation details and usage example.
- Clarified 2D/3D layout options for depiction.
- Expanded list of `extras` dependencies in installation instructions.
- New optional dependencies: Indigo and `extra-clean2d`. Updated `pyproject.toml` accordingly.

Sticky fragments (#66)

sticky smiles generation helpers.
better reactions api.
new reactions.
More tests.

fixed mapping overlap in carbonyl deprotections.

updated isomer and group standardization rules; refined backup logic …

…in molecule container

refined substructure extraction logic; optimized atom filtering, bond…

… copying, and hydrogen recalculation handling

reactor now handles extended stereo

added skip_elements support for metal handling functions; introduced …

…bond rescaling helper.

added iupac alias to opsin

added fixes for some heterocycles.