Parse optional trailing query parameters off subjects (#49)

[rossdanderson]

Closes #49.

What & why

AntPatternNamespace had no notion of an optional trailing query string on a subject, which (a) polluted the last path variable when a subject carried a ?query, and (b) left consumers no way to read query parameters. This adds first-class parsing of an optional trailing ?a=b&c=d.

Changes

datasourcex-util

• Strip an optional trailing ?query before match / extractPathVariables so path variables are never polluted (the bug fix).
• Add extractQueryParameters(subject) — parses ?a=b&c=d into a map (empty when absent), via a shared pure parseQueryString helper (URL-decoding, empty values, last-wins on repeated keys).
• URL-decode path variables too, for consistency with the Spring DataSourceMessageHandler (which already decodes destination variables).
• Expose a shared CHARSET; DataSourceServerBootstrap.bootstrapCharset sources from it.

Reactive Bind DSL

• Thread the parsed query map to all supplier shapes via a Request / ChannelRequest object (path, pathVariables, queryParameters[, receive]) instead of positional params — avoids the adjacent same-typed-map footgun and makes future field additions non-breaking.
• RequestSupplier / ChannelRequestSupplier are receiver-style SAMs (operator fun Request.invoke()): Kotlin gets { this.path } ergonomics from a single overload (no ambiguity), Java implements a clean invoke(request).
• Retain the previous positional shapes as @Deprecated PathVariablesSupplier / PathVariablesChannelSupplier overloads for source back-compat.

⚠️ Behavioural change (path-variable decoding)

Because path variables are now URL-decoded (matching the Spring handler):

• + in a value becomes a space (e.g. /RATES/USD+SOFR → USD SOFR).
• A value with a malformed/lone % (e.g. 100%) throws IllegalArgumentException.
• Literal non-ASCII (CJK/Cyrillic/accented) is unaffected.
• A query-less subject with +/% is therefore no longer byte-identical to before.

This was a deliberate call for consistency with the existing Spring destination-variable decoding.

Versioning

Additive to datasourcex-util. The reactive supplier interfaces are reshaped (deprecated overloads retained) → major bump. .api snapshots regenerated.

Testing

./gradlew --continue check green. AntPatternNamespaceTest covers pollution-fix, no/single/multiple query params, query on an exact pattern, path+query URL-decoding, empty values, and repeated keys; BindTest adds an end-to-end receiver-style + query-parameter delivery test.

Spring note

Investigated whether Spring @MessageMapping offers query parameters — it does not (only @DestinationVariable/@Header/@Headers/@Payload/Principal; no @RequestParam equivalent for messaging destinations), so this is a genuine framework extension.