Enforce SPDX licenses by default, allow opting out of semver versions

[andrius-puksta-sensmetry]

Changes

• by default, require that license is an SPDX license expression, but allow opting out
  This is implemented in CLI, but not in bindings. How should this be handled there?
• allow opting out of using a semantic version
  This is implemented in CLI, but not in bindings. Again, how should this be handled there?
• use license spelling instead of the less common licence; commands have aliases for both variants
• style: consistently use `` for quoting everything (mostly IRIs)
• use serialization instead of serialisation to match common usage other crates/ecosystems
• (Java bindings) throw an exception instead of panicking in all reasonable cases in bindings code (part of Consider replacing panics with internal errors #110)
• (Java bindings) unify our JNI extension traits to JniExt
• unify new and init commands into init; this avoids internal duplication and potential user confusion over which command to use
• always use create_dir_all() for new project dir; this means we require that the directory does not exist yet (exception for current dir is made). This matches Cargo and uv and also allows doing sysand init a/b/c/d/e/f, where none of them exist in advance

Fixes

• (Java bindings) fix std exception names
• correctly treat version requirements of packages when installing them through sysand env install
• allow using dependency options in sysand info <subcommand>
• for info subcommand, only print std lib warning when command is usage, as it's the only command that may include output about std libs

CLI improvements

• require that sysand info set <website> is supplied a valid IRI, but tolerate a missing scheme and default to https:// in that case
• improve error and log messages in many places
• use custom wrapper for current_dir() to give nicer errors
• more consistently utilize wrapfs methods where possible for better errors

Docs

• document requirements for versions, version constraints and licenses, in user guide, CLI and javadoc
• use console type for console session highlighting
• use sh instead of bash highlighting for most shell commands

Tests

• (Java bindings) check that all custom Sysand exceptions are present
• test that semver crate defaults to caret (^) version requirement
  if none is present, as we promise this behaviour

[victor-linroth-sensmetry]

I can't fully vouch for the Java stuff but it seems like it's fine. Everything else looks good too.