feat: add synchronous parseMarkdown returning a parsed State

[mvanhorn]

Description

Adds a public top-level parseMarkdown(content, lookupLinks, flavour, parser, referenceLinkHandler): State to MarkdownState.kt, sitting alongside the existing parseMarkdownFlow(...) and mirroring its parameter list and defaults. It parses on the calling thread and returns the final, immutable State directly (State.Success on success, or State.Error on failure).

Internally it builds the same Input and MarkdownStateImpl and calls the already-present parseBlocking(), so the change is purely additive and reuses every existing code path (input construction, parsing, link lookup).

Motivation: today the only non-composable parse API is parseMarkdownFlow(), which forces callers through mutable Flow/StateFlow machinery to obtain a result. There was no way to synchronously get a State.Success to hand to the Markdown composable. parseMarkdown lets you pre-parse content before the UI is shown and pass the already-parsed, immutable State straight into Markdown(state), with no mutable surface exposed to the caller.

val state = parseMarkdown("# Markdown")
Markdown(state)

Note: parsing happens on the calling thread; for large documents callers should invoke off the main thread.

Fixes #587

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation update

How Has This Been Tested?

Added ParseMarkdownTest in commonTest and ran it on the JVM target.

• ./gradlew :multiplatform-markdown-renderer:jvmTest --tests "com.mikepenz.markdown.model.ParseMarkdownTest" passes (4/4): happy path (synchronous State.Success with parsed node and original content), empty content (returns State.Success, not State.Loading), reference-link resolution with lookupLinks = true, and the error path (returns State.Error carrying the throwable instead of throwing).
• Updated the binary-compatibility .api / .klib.api dumps for the new function.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[mvanhorn]

Thank you @mikepenz. A synchronous parseMarkdown that returns a parsed State is a handy addition for callers that don't want the async path.